ci: Move rules from `.build fedora x86_64` to `.build`

ci: Move rules from `.build fedora x86_64` to `.build`

They should apply to all job that extend it as the 2 jobs that depend on
`.build` but not on `.build fedora x86_64` is
`build nodebug fedora x86_64` which pulls `build static nodebug fedora x86_64`
both jobs should be manual on `main` and they should run only if some
files "modules_changes" happened

Also make sure we do no automatically run job on `main` branches from forks

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/1141>