Bump actions/download-artifact from 7 to 8 #4335

Job	Run time
Prepare CodeQL unit test matrix	6s
Run unit tests (cpp, 2.21.4, codeql-cli/v2.21.4, codeql-bundle-v2.21.4, ubuntu-latest-xl, codeql-...	2h 11m 23s
Run unit tests (c, 2.21.4, codeql-cli/v2.21.4, codeql-bundle-v2.21.4, ubuntu-latest-xl, codeql-cl...	40m 24s
Validate test results	11s
	2h 52m 4s

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