ci: Migrate to GitHub Actions and reusable workflows, part two #2

Job	Run time
Swift 6 Language Mode	0s
Integration test / Linux (5.8)	23s
Integration test / Linux (5.9)	1m 2s
Integration test / Linux (5.10)	1m 4s
Integration test / Linux (nightly-6.0)	1m 4s
Integration test / Linux (nightly-main)	26s
Soundness / API breakage check	1m 14s
Soundness / Broken symlinks check	2s
Soundness / Documentation check	38s
Soundness / Format check	34s
Soundness / License headers check	4s
Soundness / Shell check	30s
Soundness / Unacceptable language check	2s
Unit tests / Unit tests / Linux (5.8)	23s
Unit tests / Unit tests / Linux (5.9)	1m 0s
Unit tests / Unit tests / Linux (5.10)	58s
Unit tests / Unit tests / Linux (nightly-6.0)	1m 3s
Unit tests / Unit tests / Linux (nightly-main)	27s
	10m 54s

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