Use Django's `LiveServerTestCase` for frontend tests #3841

Job	Run time
Test + Coverage	2m 46s
MyPy	1m 34s
Test Frontend	3m 12s
Build wheel	1m 41s
Test (shuffled order)	2m 31s
Test if testdata is up to date	2m 1s
Backup process	2m 55s
Compile Scss	1m 40s
Formatting	1m 35s
Linter	2m 10s
Build nix environment on MacOS	2m 51s
Install wheel with system Python	10s
	25m 6s

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