Ensure case contact form selects klanten backend from API group #9108

Job	Run time
Build and check documentation	1m 33s
End-to-end tests, chromium	2m 10s
Run the Django test suite (main)	2m 58s
End-to-end tests, firefox	2m 58s
Run the Django test suite (elastic)	2m 57s
End-to-end tests, webkit	2m 6s
Run the Django test suite (openklant)	2m 48s
End-to-end tests, msedge	3m 0s
Run the Django test suite (sequential)	2m 58s
Upload coverage information to codecov	1s
Build (and push) Docker image	1s
	23m 30s

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