Add workflow permissions #3941

Job	Run time
Prepare CodeQL unit test matrix	5s
Run unit tests (cpp, 2.20.7, codeql-cli/v2.20.7, codeql-bundle-v2.20.7, ubuntu-latest-xl, codeql-...	1h 40m 58s
Run unit tests (c, 2.20.7, codeql-cli/v2.20.7, codeql-bundle-v2.20.7, ubuntu-latest-xl, codeql-cl...	35m 40s
Validate test results	5s
	2h 16m 48s

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