Ok, so seems that PR25188 works if the abi dump file for the "correct" version is generated with the same compiler that is used to check the ABI. I think this is acceptable if the workflow is:
- As soon as a version is released, we generate in the stable release branch the dump using some docker container with the same compiler as the GitHub CI.
- We enable the ABI check only for release branches.
- We should make the check mandatory because release managers cannot be checking all backport PRs unfortunately.
We make the changes for 3.8 and 3.9 for the time being.