Rename ~pipeline:expedite-master-fixing label to ~pipeline:expedite

Context

This issue implements step 1 of gitlab-org/ruby/gems/gitlab-dangerfiles#28 (comment 1209372811).

gitlab-org/ruby/gems/gitlab-dangerfiles!135 (comment 1209117246)

We would like to use ~"pipeline:expedite-master-fixing" label with revert MRs as well.

Goal

Change the label name from ~"pipeline:expedite-master-fixing" to pipeline:expedite, so that we can use both use-cases (master-broken and revert MRs).