Fix regex for octal literal matching #4742

Job	Run time
Prepare CodeQL unit test matrix	6s
Run unit tests (c, 2.21.4, codeql-cli/v2.21.4, codeql-bundle-v2.21.4, ubuntu-latest-xl, codeql-cl...	45m 2s
Run unit tests (cpp, 2.21.4, codeql-cli/v2.21.4, codeql-bundle-v2.21.4, ubuntu-latest-xl, codeql-...	2h 26m 42s
Validate test results	4s
	3h 11m 54s

Provide feedback