Tests

Add support for Swift 5.9, drop support for older Swift versions #259

Job	Run time
variables	3s
test-spm (macOS, 0) / determine-versions	3s
test-xcode (macOS, 0) / determine-versions	2s
test-xcode (iPadOS, 0) / determine-versions	9s
test-xcode (iOS, 0) / determine-versions	10s
test-xcode (watchOS, 0) / determine-versions	4s
test-xcode (tvOS, 0) / determine-versions	3s
test-xcode (macOS, 0) / run-tests	4m 5s
test-xcode (tvOS, 0) / run-tests	6m 27s
test-xcode (watchOS, 0) / run-tests	7m 2s
test-spm (macOS, 0) / run-tests	1m 44s
test-xcode (iOS, 0) / run-tests	9m 49s
test-xcode (iPadOS, 0) / run-tests	5m 54s
	35m 35s

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