Allow specifying a tag that should be used as a baseline for API breakage checks #118

Job	Run time
Test with Docker / Linux (5.8 - jammy)	29s
Test with Docker / Windows (5.9 - windows-2022)	14m 53s
Test with Docker / Linux (5.9 - jammy)	28s
Test without Docker / Windows (5.9 - windows-2022)	6m 13s
Test with Docker / Windows (6.0 - windows-2022)	17m 31s
Test without Docker / Linux (${{ matrix.swift_version }} - ${{ matrix.os_version }})	0s
Test with Docker / Linux (5.10 - jammy)	31s
Test without Docker / Windows (6.0 - windows-2022)	6m 1s
Test with Docker / Windows (nightly - windows-2019)	9m 27s
Test with Docker / Linux (6.0 - jammy)	34s
Test without Docker / Windows (nightly - windows-2022)	3m 39s
Test with Docker / Windows (nightly-6.1 - windows-2019)	8m 23s
Test with Docker / Linux (nightly-main - jammy)	36s
Test without Docker / Windows (nightly-6.1 - windows-2022)	3m 10s
Test with Docker / Linux (nightly-6.1 - jammy)	35s
Soundness / API breakage check	0s
Soundness / Documentation check	42s
Soundness / Broken symlinks check	3s
Soundness / Format check	0s
Soundness / License headers check	3s
Soundness / Python lint check	4s
Soundness / Shell check	33s
Soundness / Unacceptable language check	3s
Soundness / YAML lint check	3s
	1h 14m 1s

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