[docker ci] Split up amd64 (x86_64) and arm64 builds (#4054)

* [docker ci] Split up amd64 (x86_64) and arm64 builds

- Lets run them seperately to cut down total time
- Will also more clearly show if either arch has specific problems
- Kept amd64 (x86_64) using qemu actions so if GitHub ever offers arm64 boxes it could stay working too

Fixes #3971

* Add CHANGES entry

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Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>