Improve error reporting on config migration #6795

Job	Run time
check-codebase	24s
check-required-label	2s
build	1m 9s
Integration Tests - git 2.20.0	1m 22s
lint	37s
Integration Tests - git 2.22.5	1m 11s
Integration Tests - git 2.23.0	1m 12s
Integration Tests - git 2.25.1	1m 14s
check-for-fixups	5s
Integration Tests - git 2.30.8	1m 9s
Integration Tests - git latest	1m 19s
ci - ubuntu-latest	35s
ci - windows-latest	2m 59s
upload-coverage	0s
	13m 18s

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