Update SwiftSyntax and support Swift 5.4.2 and 5.5 in CI

[uhooi]

Overview

• Update SwiftSyntax
• Support Swift 5.4.2 and 5.5 in CI

References

• https://github.com/apple/swift-syntax/releases/tag/0.50500.0
• https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#jobsjob_idstrategymatrix
• https://github.com/yonaskolb/XcodeGen/blob/12511afed82a3db1a9dbd814e835920c98d9914e/.github/workflows/ci.yml