Ensure case contact form selects klanten backend from API group #9107

Job	Run time
Run the Django test suite (main)	16m 50s
Build and check documentation	1m 51s
End-to-end tests, chromium	4m 46s
Run the Django test suite (elastic)	6m 42s
End-to-end tests, firefox	4m 23s
Run the Django test suite (openklant)	2m 59s
End-to-end tests, webkit	4m 52s
Run the Django test suite (sequential)	5m 46s
End-to-end tests, msedge	5m 7s
Upload coverage information to codecov	1s
Build (and push) Docker image	1s
	53m 18s

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