Steps: (See: https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow#running-a-workflow)

1. Fork the adafruit/circuitpython repository.
2. Activate GitHub Actions in your fork.
3. Select "Custom board build" workflow.
4. Click on "Run workflow".
5. You will be presented with the following menu.

Menu:

• Board:
  • The board_id of the board to build.
  • Can be found in ports/*/boards/[board_id]
• Version:
  • The version of CircuitPython to build.
  • Can be a tag or a commit. Anything above c8a325a should work but >=8.1.0 is better to communicate.
• Language:
  • The language of the build.
  • Can be found in locale/[language].po
• Flags:
  • The flags to use for the build.
  • Example: CIRUITPY_WIFI=1.
• Debug:
  • Whether or not to make a debug build.
  • Check the box to make a debug build.

The resulting build command executed in the port directory:

make -j2 $FLAGS BOARD=... DEBUG=... TRANSLATION=...

The generated build-*/firmware.* files will be available as an artifact.

Note
The firmware version will have -dirty appended to it if the flags are provided or it is a debug build.

Related to #4552.

Also fixes main merge builds not being uploaded to AWS S3. (per discord discussion)