Ci set matrix improvements

[jepler]

This runs faster, is more correct (I hope!) and is easier to test locally. Closes #6922

Frozen modules:

$ GITHUB_OUTPUT=/dev/null ./tools/ci_set_matrix.py  frozen/Adafruit_CircuitPython_MIDI 
Using files list on commandline
Adding docs/boards to build based on changed files
Building docs: False
Building boards:
  zrichard_rp2.65-f

Port-specific changes to shared modules:

$ GITHUB_OUTPUT=/dev/null ./tools/ci_set_matrix.py  ports/raspberrypi/common-hal/ssl/SSLSocket.c 
Using files list on commandline
Adding docs/boards to build based on changed files
Building docs: False
Building boards:
  raspberry_pi_pico_w

Changes to port-specific modules:

$ GITHUB_OUTPUT=/dev/null ./tools/ci_set_matrix.py  ports/raspberrypi/bindings/cyw43/__init__.c
Using files list on commandline
Adding docs/boards to build based on changed files
Building docs: True
Building boards:
  raspberry_pi_pico_w

[dhalbert]

Thanks for this good cleanup!