ci: nix caches cause the 10GB cache space to be used up quickly, slowing down Github actions

[JakobLichterfeld]

Introducing the cleanup caches job on merge helped, but was not enough: 0dd5ef1

[JakobLichterfeld]

I do run a gh cache delete --allright now once again as a workaround

[JakobLichterfeld]

as of October 21st:

This extension should be removed and replaced with usage of gh cache directly (see: https://github.com/actions/gh-actions-cache)

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• ci(fix): update cleanup_caches.yml to use new cache management commands and fix permissions (d6793ce, b0b694f, 16bb503 - @JakobLichterfeld)
• ci: Add workflow to manually cleanup largest 100 caches (dad7e3d, 523419d - @JakobLichterfeld)