Can arm and disarm with mavutil but can't override rc channels.

Hello,

I'm currently using Pymavlink (specifically the mavutil functions) to try and arm and then override the rc channels but it is not fully working. I am able to arm the quadcopter and it spins up the motors to the default speed but then I try to have rc channels overridden but it doesn't do anything and I also don't get any errors saying that it didn't go through. Here is general idea of how my code works:

```
from pymavlink import mavutil as mavutil

m = mavutil.mavlink_connection(connection, baud=111100)
m.mav.command_long_send(
m.target_system,
m.target_component,
mavutil.mavlink.MAV_CMD_COMPONENT_ARM_DISARM,
0,
1,
0,
0,
0,
0,
0,
0,
)
rc_channel_values = [65535 for _ in range(18)]
rc_channel_values[0:4] = [1900, 1900, 1900, 1900]
m.mav.rc_channels_override_send(
m.target_system, # target_system
m.target_component, # target_component
*rc_channel_values, # RC channel list, in microseconds.
)
```

I've been banging my head against the wall trying to reverse engineer all the code and documentation to fix it but I'm really not getting anywhere. I don't even know how to debug the whole system, it just either works or it doesn't. Any help would be greatly appreciated, thanks!

Start by reproducing the supplied Python example through mavutil.mavlink_connection and rc_channels_override_send, then trace how the RC override message is sent and acknowledged. The report names no repository file or test, so first identify the relevant mavutil entry point and existing coverage; done means explaining why the override is ignored or adding a verified fix and regression test.

Written by the indexing model from the issue text.