C++: Fix queries after shared guards #3829

Job	Run time
Prepare CodeQL unit test matrix	5s
Run unit tests (c, 2.20.7, codeql-cli/v2.20.7, codeql-bundle-v2.20.7, ubuntu-latest-xl, codeql-cl...	14m 34s
Run unit tests (cpp, 2.20.7, codeql-cli/v2.20.7, codeql-bundle-v2.20.7, ubuntu-latest-xl, codeql-...	1h 38m 43s
Validate test results	4s
	1h 53m 26s

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