Test mismatching testdata #3779

Job	Run time
Test + Coverage	2m 45s
MyPy	1m 33s
Formatting	1m 30s
Test (shuffled order)	2m 21s
Linter	1m 25s
Reject testdata changes	1m 26s
Backup process	3m 6s
Compile Scss	1m 32s
Build nix environment on MacOS	3m 25s
Render Html pages	1m 53s
Test Typescript	1m 55s
	22m 51s

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