getFileDiffsWithBasehead(): use CODE_SCANNING_REPOSITORY if present #4626

Job	Run time
Go: tracing with autobuilder step (ubuntu-latest, stable-v2.19.4)	1m 22s
Go: tracing with autobuilder step (ubuntu-latest, stable-v2.15.5)	1m 25s
Go: tracing with autobuilder step (macos-latest, linked)	3m 25s
Go: tracing with autobuilder step (macos-latest, default)	3m 6s
Go: tracing with autobuilder step (ubuntu-latest, stable-v2.18.4)	1m 31s
Go: tracing with autobuilder step (macos-latest, stable-v2.19.4)	3m 37s
Go: tracing with autobuilder step (macos-latest, stable-v2.16.6)	3m 28s
Go: tracing with autobuilder step (ubuntu-latest, default)	1m 15s
Go: tracing with autobuilder step (ubuntu-latest, stable-v2.17.6)	1m 27s
Go: tracing with autobuilder step (macos-latest, stable-v2.18.4)	4m 46s
Go: tracing with autobuilder step (macos-latest, stable-v2.17.6)	2m 49s
Go: tracing with autobuilder step (ubuntu-latest, linked)	1m 10s
Go: tracing with autobuilder step (macos-latest, nightly-latest)	3m 34s
Go: tracing with autobuilder step (ubuntu-latest, nightly-latest)	1m 18s
Go: tracing with autobuilder step (ubuntu-latest, stable-v2.16.6)	1m 20s
Go: tracing with autobuilder step (macos-latest, stable-v2.15.5)	3m 7s
	38m 40s

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