Same happens with spot_real.launch:

on@jon-noetic:~/catkin_ws$ roslaunch mini_ros spot_real.launch
... logging to /home/jon/.ros/log/4d0e42a6-cde7-11eb-8559-f11a37245d28/roslaunch-jon-noetic-30900.log
Checking log directory for disk usage. This may take a while.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://jon-noetic:36887/

SUMMARY

PARAMETERS

• /BaseClearanceHeight: 0.035
• /BasePenetrationDepth: 0.003
• /BaseStepVelocity: 0.001
• /CD_SCALE: 0.05
• /CHPD_SCALE: 0.0005
• /ClearanceHeight_LIMITS: [0.0, 0.04]
• /PenetrationDepth_LIMITS: [0.0, 0.02]
• /RESIDUALS_SCALE: 0.015
• /RPY_SCALE: 0.785
• /SLV_SCALE: 0.05
• /STEPLENGTH_SCALE: 0.05
• /SV_SCALE: 0.05
• /SwingPeriod_LIMITS: [0.1, 0.3]
• /Tswing: 0.2
• /YAW_SCALE: 1.25
• /Z_SCALE: 0.035
• /Z_SCALE_CTRL: 0.15
• /actions_to_filter: 14
• /agent_num: 0
• /alpha: 0.7
• /com_offset: 0.0
• /dt: 0.001
• /elbow_length: 0.10652
• /foot_x: 0.23
• /foot_y: 0.185
• /height: 0.2
• /hip_x: 0.23
• /hip_y: 0.075
• /rosdistro: noetic
• /rosversion: 1.15.11
• /serial_node/baud: 500000
• /serial_node/port: /dev/ttyS0
• /shoulder_length: 0.055
• /spot_joy/deadzone: 0.005
• /spot_joy/dev: /dev/input/js0
• /spot_sm/frequency: 200.0
• /spot_teleop/axis_angular: 0
• /spot_teleop/axis_linear_x: 4
• /spot_teleop/axis_linear_y: 3
• /spot_teleop/axis_linear_z: 1
• /spot_teleop/button_estop: 1
• /spot_teleop/button_switch: 0
• /spot_teleop/frequency: 200.0
• /spot_teleop/scale_angular: 1.0
• /spot_teleop/scale_linear: 1.0
• /wrist_length: 0.145

NODES
/
serial_node (rosserial_python/serial_node.py)
spot_joy (joy/joy_node)
spot_real (mini_ros/spot_real_interface)
spot_sm (mini_ros/spot_sm)
spot_teleop (mini_ros/teleop_node)

ROS_MASTER_URI=http://localhost:11311

process[spot_sm-1]: started with pid [30914]
process[spot_joy-2]: started with pid [30915]
[ INFO] [1623772430.923082346]: STARTING NODE: spot_mini State Machine
process[spot_teleop-3]: started with pid [30916]
[ INFO] [1623772430.930437359]: STARTING NODE: Teleoperation
process[spot_real-4]: started with pid [30921]
/usr/bin/env: ‘python’: No such file or directory
process[serial_node-5]: started with pid [30927]
[ERROR] [1623772430.943202662]: Couldn't open joystick /dev/input/js0. Will retry every second.
[spot_real-4] process has died [pid 30921, exit code 127, cmd /home/jon/catkin_ws/src/mini_ros/src/spot_real_interface __name:=spot_real __log:=/home/jon/.ros/log/4d0e42a6-cde7-11eb-8559-f11a37245d28/spot_real-4.log].
log file: /home/jon/.ros/log/4d0e42a6-cde7-11eb-8559-f11a37245d28/spot_real-4*.log
[ERROR] [1623772431.267400, 0.000000]: Error opening serial: [Errno 13] could not open port /dev/ttyS0: [Errno 13] Permission denied: '/dev/ttyS0'
[ERROR] [1623772434.272595, 0.000000]: Error opening serial: [Errno 13] could not open port /dev/ttyS0: [Errno 13] Permission denied: '/dev/ttyS0'
[ERROR] [1623772437.279337, 0.000000]: Error opening serial: [Errno 13] could not open port /dev/ttyS0: [Errno 13] Permission denied: '/dev/ttyS0'
[ERROR] [1623772440.286008, 0.000000]: Error opening serial: [Errno 13] could not open port /dev/ttyS0: [Errno 13] Permission denied: '/dev/ttyS0'
[ERROR] [1623772443.292706, 0.000000]: Error opening serial: [Errno 13] could not open port /dev/ttyS0: [Errno 13] Permission denied: '/dev/ttyS0'
^C[serial_node-5] killing on exit
[spot_teleop-3] killing on exit
[spot_sm-1] killing on exit
[spot_joy-2] killing on exit
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/serial/serialposix.py", line 265, in open
self.fd = os.open(self.portstr, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)
PermissionError: [Errno 13] Permission denied: '/dev/ttyS0'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/opt/ros/noetic/lib/python3/dist-packages/rosserial_python/SerialClient.py", line 374, in init
self.port = Serial(port, baud, timeout=self.timeout, write_timeout=10)
File "/usr/lib/python3/dist-packages/serial/serialutil.py", line 240, in init
self.open()
File "/usr/lib/python3/dist-packages/serial/serialposix.py", line 268, in open
raise SerialException(msg.errno, "could not open port {}: {}".format(self._port, msg))
serial.serialutil.SerialException: [Errno 13] could not open port /dev/ttyS0: [Errno 13] Permission denied: '/dev/ttyS0'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/opt/ros/noetic/lib/python3/dist-packages/rospy/core.py", line 572, in signal_shutdown
h()
File "/opt/ros/noetic/lib/python3/dist-packages/rosserial_python/SerialClient.py", line 354, in shutdown
self.txStopRequest()
File "/opt/ros/noetic/lib/python3/dist-packages/rosserial_python/SerialClient.py", line 422, in txStopRequest
self.port.flushInput()
AttributeError: 'SerialClient' object has no attribute 'port'
shutting down processing monitor...
... shutting down processing monitor complete
done

from spot_mini_mini.

Fixed it by changing first line to:
#!/usr/bin/env python3

from spot_mini_mini.