Add trailing comma support in cases missing from Swift 6.1 #202

Job	Run time
Run tests using swift-syntax-dev-utils (Linux)	23m 11s
Run tests using swift-syntax-dev-utils (Windows)	48m 6s
Validate generated code	2m 43s
Test / Linux (5.9 - jammy)	3m 51s
Test / Linux (5.10 - jammy)	3m 45s
Test / Linux (6.0 - jammy)	3m 59s
Test / Linux (6.1 - jammy)	3m 54s
Test / Linux (nightly-main - jammy)	4m 44s
Test / Linux (nightly-6.1 - jammy)	4m 32s
Test / macOS (Xcode ${{ matrix.xcode_version }} - ${{ matrix.os_version }} - ${{ matrix.arch }})	0s
Test / Windows (5.9 - windows-2022)	25m 16s
Test / Windows (6.0 - windows-2022)	21m 49s
Test / Windows (6.1 - windows-2022)	23m 52s
Test / Windows (nightly - windows-2019)	15m 15s
Test / Windows (nightly-6.1 - windows-2019)	15m 25s
Soundness / API breakage check	0s
Soundness / Documentation check	4m 52s
Soundness / Unacceptable language check	4s
Soundness / Broken symlinks check	3s
Soundness / Format check	40s
Soundness / License headers check	9s
Soundness / Shell check	33s
Soundness / YAML lint check	4s
Soundness / Python lint check	4s
	3h 26m 51s

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