[GHA] Only format Swift files that are in Git index #158

Job	Run time
Soundness / API breakage check	27s
Cxx interop / 5.8	1m 2s
Integration tests / 5.8	13m 4s
Benchmarks / 5.8	2m 41s
Cxx interop / 5.9	1m 15s
Integration tests / 5.9	14m 42s
Benchmarks / 5.9	3m 40s
Cxx interop / 5.10	1m 14s
Integration tests / 5.10	14m 17s
Benchmarks / 5.10	3m 39s
Cxx interop / nightly-6.0	1m 45s
Soundness / Broken symlinks check	2s
Integration tests / nightly-6.0	16m 53s
Benchmarks / nightly-6.0	5m 6s
Cxx interop / nightly-main	1m 44s
Integration tests / nightly-main	17m 36s
Benchmarks / nightly-main	5m 8s
Soundness / Documentation check	1m 59s
Soundness / Format check	30s
Soundness / License headers check	8s
Soundness / Unacceptable language check	2s
Unit tests / 5.8	3m 9s
Unit tests / 5.9	3m 24s
Unit tests / 5.10	3m 11s
Unit tests / nightly-6.0	4m 15s
Unit tests / nightly-main	4m 6s
	2h 4m 59s

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