Case-independent GCode file extensions #905

Job	Run time
tests (ubuntu-latest, tests)	2m 42s
build (ubuntu-latest, noradio)	1m 50s
tests (macos-latest, tests)	47s
build (ubuntu-latest, wifi)	2m 11s
tests (windows-latest, tests_nosan)	1m 30s
build (ubuntu-latest, bt)	2m 3s
build (macos-latest, noradio)	2m 36s
build (macos-latest, wifi)	2m 2s
build (macos-latest, bt)	2m 5s
build (windows-latest, noradio)	3m 59s
build (windows-latest, wifi)	5m 12s
build (windows-latest, bt)	5m 33s
	32m 30s

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