ci: skip lintcommit workflow on release branches

Since lintcommit is a required check, it will always need to be run.
However, the lintcommit script is not designed to work on PRs that
doesn't target master branch (and it's not clear whether it's even
desirable).

To circumvent this we create a "dummy" lintcommit check that is run on
release branches that always passes, thus fulfilling the condition of
the required check.

.github/workflows/lintcommit.yml

@@ -1,10 +1,9 @@
-name: "lintcommit"
+name: lintcommit
 on:
   pull_request:
     types: [opened, synchronize, reopened, ready_for_review]
     branches:
       - 'master'
-      - 'release-[0-9]+.[0-9]+'
 jobs:
   lint-commits:
     runs-on: ubuntu-latest