[6.2] Relax precondition in `postProcessMultilineStringLiteral` #242

Job	Run time
Validate generated code	2m 59s
Run tests using swift-syntax-dev-utils (Linux)	24m 22s
Test / Windows (6.0 - windows-2022)	22m 3s
Test / Windows (nightly - windows-2019)	16m 21s
Test / Linux (5.10 - jammy)	4m 5s
Test / Linux (nightly-main - jammy)	4m 47s
Test / Windows (5.9 - windows-2022)	23m 45s
Test / Linux (6.0 - jammy)	4m 3s
Test / Windows (6.1 - windows-2022)	26m 24s
Test / Linux (5.9 - jammy)	4m 1s
Test / Linux (6.1 - jammy)	4m 26s
Test / Linux (nightly-6.1 - jammy)	4m 45s
Run tests using swift-syntax-dev-utils (Windows)	42m 23s
Test / Linux (nightly-6.2 - jammy)	4m 44s
Test / Windows (nightly-6.1 - windows-2019)	14m 40s
Test / macOS (Xcode ${{ matrix.xcode_version }} - ${{ matrix.os_version }} - ${{ matrix.arch }})	0s
Soundness / Format check	37s
Soundness / Python lint check	10s
Soundness / Shell check	37s
Soundness / API breakage check	0s
Soundness / Unacceptable language check	5s
Soundness / License headers check	12s
Soundness / Broken symlinks check	12s
Soundness / Documentation check	4m 59s
Soundness / YAML lint check	4s
	3h 30m 44s

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