Fix a crash if we had a dollar identifier as the second parameter label in a closure not followed by a colon #238

Job	Run time
Validate generated code	2m 50s
Run tests using swift-syntax-dev-utils (Linux)	24m 7s
Run tests using swift-syntax-dev-utils (Windows)	43m 1s
Test / Linux (5.9 - jammy)	3m 54s
Test / Linux (5.10 - jammy)	3m 51s
Test / Linux (nightly-6.1 - jammy)	4m 52s
Test / Linux (6.1 - jammy)	4m 10s
Test / Linux (6.0 - jammy)	4m 14s
Test / Linux (nightly-main - jammy)	4m 48s
Test / Linux (nightly-6.2 - jammy)	4m 48s
Test / Windows (6.1 - windows-2022)	19m 4s
Test / Windows (6.0 - windows-2022)	15m 30s
Test / Windows (5.9 - windows-2022)	17m 3s
Test / Windows (nightly - windows-2019)	17m 55s
Test / Windows (nightly-6.1 - windows-2019)	16m 3s
Soundness / License headers check	11s
Soundness / Shell check	35s
Soundness / Format check	41s
Soundness / Broken symlinks check	5s
Soundness / Unacceptable language check	4s
Soundness / Documentation check	4m 52s
Soundness / API breakage check	0s
Soundness / Python lint check	11s
Soundness / YAML lint check	4s
Test / macOS (Xcode ${{ matrix.xcode_version }} - ${{ matrix.os_version }} - ${{ matrix.arch }})	0s
	3h 12m 53s

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