Drop support for Swift 5.8 #6

Job	Run time
Soundness / Broken symlinks check	2s
Soundness / API breakage check	1m 56s
Soundness / License headers check	6s
Soundness / Documentation check	1m 37s
Soundness / Unacceptable language check	5s
Soundness / YAML lint check	4s
Soundness / Format check	0s
Soundness / Python lint check	0s
Soundness / Shell check	0s
Unit tests / Unit tests / Linux (5.9)	3m 10s
Unit tests / Unit tests / Windows (nightly-6.0)	3s
Unit tests / Unit tests / Windows (6.0)	3s
Unit tests / Unit tests / Linux (5.10)	3m 16s
Unit tests / Unit tests / Windows (nightly-main)	3s
Unit tests / Unit tests / Linux (6.0)	2m 47s
Unit tests / Unit tests / Linux (nightly-6.0)	3m 14s
Cxx interop / Cxx interop / Windows (6.0)	2s
Cxx interop / Cxx interop / Linux (5.9)	1m 14s
Cxx interop / Cxx interop / Windows (nightly-6.0)	2s
Unit tests / Unit tests / Linux (nightly-main)	3m 32s
Cxx interop / Cxx interop / Linux (5.10)	1m 14s
Cxx interop / Cxx interop / Windows (nightly-main)	2s
Cxx interop / Cxx interop / Linux (6.0)	1m 23s
Cxx interop / Cxx interop / Linux (nightly-6.0)	1m 46s
Cxx interop / Cxx interop / Linux (nightly-main)	1m 40s
	27m 21s

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