getFileDiffsWithBasehead(): use CODE_SCANNING_REPOSITORY if present #6705

Job	Run time
Packaging: Config file (macos-latest, nightly-latest)	1m 26s
Packaging: Config file (macos-latest, linked)	1m 5s
Packaging: Config file (windows-latest, default)	10m 27s
Packaging: Config file (windows-latest, nightly-latest)	6m 35s
Packaging: Config file (macos-latest, default)	1m 16s
Packaging: Config file (ubuntu-latest, nightly-latest)	1m 25s
Packaging: Config file (ubuntu-latest, default)	1m 19s
Packaging: Config file (ubuntu-latest, linked)	1m 22s
Packaging: Config file (windows-latest, linked)	9m 2s
	33m 57s

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