Case-independent GCode file extensions #906

Job	Run time
tests (ubuntu-latest, tests)	2m 46s
build (ubuntu-latest, noradio)	1m 52s
tests (macos-latest, tests)	46s
build (ubuntu-latest, wifi)	2m 9s
tests (windows-latest, tests_nosan)	1m 26s
build (ubuntu-latest, bt)	2m 1s
build (macos-latest, noradio)	1m 54s
build (macos-latest, wifi)	1m 53s
build (macos-latest, bt)	1m 54s
build (windows-latest, noradio)	4m 36s
build (windows-latest, wifi)	5m 44s
build (windows-latest, bt)	4m 51s
	31m 52s

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