Add better error messages when determining merge-base #2707

Job	Run time
Use a custom `checkout_path` (ubuntu-latest, stable-20220615)	4m 7s
Use a custom `checkout_path` (macos-latest, stable-20220615)	6m 21s
Use a custom `checkout_path` (windows-latest, stable-20220615)	10m 4s
Use a custom `checkout_path` (ubuntu-latest, stable-20220908)	3m 36s
Use a custom `checkout_path` (macos-latest, stable-20220908)	6m 2s
Use a custom `checkout_path` (windows-latest, stable-20220908)	9m 47s
Use a custom `checkout_path` (ubuntu-latest, stable-20221211)	8m 8s
Use a custom `checkout_path` (macos-latest, stable-20221211)	9m 52s
Use a custom `checkout_path` (windows-latest, stable-20221211)	13m 33s
Use a custom `checkout_path` (ubuntu-latest, stable-20230418)	3m 41s
Use a custom `checkout_path` (macos-latest, stable-20230418)	8m 55s
Use a custom `checkout_path` (windows-latest, stable-20230418)	8m 21s
Use a custom `checkout_path` (ubuntu-latest, default)	4m 58s
Use a custom `checkout_path` (macos-latest, default)	6m 31s
Use a custom `checkout_path` (windows-latest, default)	10m 2s
Use a custom `checkout_path` (ubuntu-latest, latest)	4m 51s
Use a custom `checkout_path` (macos-latest, latest)	7m 9s
Use a custom `checkout_path` (windows-latest, latest)	10m 4s
Use a custom `checkout_path` (ubuntu-latest, nightly-latest)	3m 37s
Use a custom `checkout_path` (macos-latest, nightly-latest)	16m 55s
Use a custom `checkout_path` (windows-latest, nightly-latest)	6m 33s
	2h 43m 7s

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