[#5074] Transform data for `selectboxes` in the registrations (variables tab) #15650

Job	Run time
Run the Django test suite	7m 32s
Run the Django test suite in reverse	5m 40s
Build and check documentation	1m 32s
End-to-end tests, chromium	14m 7s
End-to-end tests, firefox	18m 40s
Set up docker build 'dynamic' env variables	3s
End-to-end tests, webkit	14m 42s
docker_build (production) / Build image	2m 50s
docker_build (extensions, token_exchange,prefill_haalcentraalhr, all-extensions-) / Build image	2m 53s
Scan docker image	2m 37s
Simulate upgrading instances (3.0.1)	1m 28s
Check for unexepected OAS changes	7s
Validate OAS	15s
Generate SDKs from OAS	31s
Generate Postman collection from OAS	12s
Push Docker image	0s
update-docker-readme	0s
	1h 13m 9s

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