gitlab-ci: replace '$os' tags with '$os-x86_64' on 3.25 release branch
The latter tags are now available on our CI runners to more explicitly
distinguish `linux-x86_64` from `linux-aarch64` and to distinguish
`{macos,windows}-x86_64` from `{macos,windows}-arm64`.
This backports commit 33fe37a660 (gitlab-ci: replace '{macos,windows}'
tags with '{macos,windows}-x86_64', 2022-11-30) and commit 94d82d91d5
(gitlab-ci: replace 'linux' tags with 'linux-x86_64', 2022-11-30) to
the 3.25 release branch.