[9.20] fix: ci: Read the Docs picking old version when stable tag is updated

Read the Docs fails to pick the latest version when updating the `stable` tag, i.e. a build is triggered but it takes the previous version of it. This is a known bug in RtD: https://github.com/readthedocs/readthedocs.org/issues/10838.

The only approach that seems to solve this on our end, is to wait some time and trigger the build again so that it picks the latest version of the tag.

Backport of MR !11475

Merge branch 'backport-andoni/fix-rtd-picking-old-version-when-stable-branch-update-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!11476