Move tests in `swift-formatTests` to `SwiftFormatTests` #21

Job	Run time
Test / Linux (5.8 - jammy)	2m 2s
Test / Linux (5.9 - jammy)	2m 9s
Test / Linux (5.10 - jammy)	2m 10s
Test / Linux (6.0 - jammy)	2m 28s
Test / Linux (nightly-main - jammy)	4m 0s
Test / Linux (nightly-6.0 - jammy)	2m 57s
	15m 46s

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