Closes: #16408

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Let's explicitly allow submitting a branch immediately after running the
relevant test suite scenarios locally. This should make it possible for
a developer to start working on a ticket and submit the resulting branch for QA
in one single work session: while the branch builds on Jenkins, one can run the
relevant test suite scenarios locally. I hope this can lower the amount of WIP
developers carry and the number of context switches they have to do
(refs: #15864).

Worst case, we'll notice any test suite regression after the merge;
we can then revert the merge and nicely ask the branch submitter
to fix the regression before we merge it again.

Make release notes writing instructions consistent with the implicit expectations of our release process doc (Closes: #16586)

Our release process assumes that tech writers will push the release notes
directly to the $WEBSITE_RELEASE_BRANCH (web/release-${TAG:?}) branch. But the
tech writers doc told them to do something else. Let's resolve this conflict.

Release process: generate the expected OpenPGP signature verification output in a more deterministic way (refs: #16585)

Using --trusted-key avoids this warning:

  gpg: WARNING: This key is not certified with a trusted signature!
  gpg:          There is no indication that the signature belongs to the owner.

… and makes our signing key trusted at the "ultimate" level.

So let's also s/ultimate/full/ to stick closer to what users should
get once they verify our key via the WoT and certify it locally.

Thanks to u for the feedback!

Thanks to u for the feedback!