[CI] drop Swift 5.8 #268

Job	Run time
Integration Tests / Test archive plugin	2m 22s
Soundness / API breakage check	1m 39s
Integration Tests / Test Examples/HelloWorld on 6.0.1-amazonlinux2	1m 11s
Soundness / Documentation check	3m 43s
Integration Tests / Test Examples/APIGateway on 6.0.1-amazonlinux2	1m 20s
Soundness / Broken symlinks check	4s
Soundness / Format check	1m 0s
Integration Tests / Test Examples/S3_AWSSDK on 6.0.1-amazonlinux2	3m 50s
Soundness / License headers check	4s
Integration Tests / Test Examples/S3_Soto on 6.0.1-amazonlinux2	4m 35s
Soundness / Unacceptable language check	3s
Soundness / YAML lint check	3s
Swift 6 Language Mode / Swift 6 language mode	1m 7s
Soundness / Shell check	0s
Soundness / Python lint check	0s
Unit tests / Unit tests / Linux (5.9)	25s
Unit tests / Unit tests / Linux (5.10)	24s
Unit tests / Unit tests / Linux (6.0)	2m 42s
Unit tests / Unit tests / Linux (nightly-6.0)	2m 57s
Unit tests / Unit tests / Linux (nightly-main)	1m 58s
	29m 27s

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