[test] Migrate unit tests to Swift Testing #75

Job	Run time
Semantic Version label check	5s
Unit tests / Construct unit test matrix	3s
Swift 6 Language Mode / Swift 6 language mode	52s
Soundness / Shell check	32s
Soundness / API breakage check	1m 12s
Soundness / Unacceptable language check	5s
Soundness / License headers check	4s
Soundness / YAML lint check	4s
Soundness / Broken symlinks check	3s
Soundness / Format check	34s
Soundness / Documentation check	36s
Soundness / Python lint check	5s
Unit tests / Unit tests / Linux (nightly-main)	1m 19s
Unit tests / Unit tests / Linux (nightly-next)	1m 18s
Unit tests / Unit tests / Linux (6.1)	1m 0s
Unit tests / Unit tests / Linux (6.0)	1m 8s
	9m 0s

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