If a PR needs an approved CSR in order to be integrated, and if the PR branch is out of date with the target branch such that the JBS fix version in the .jcheck/conf file does not match that of the target branch, the bot will fail to match the approved CSR, since it will be looking for an approved CSR with the wrong fix version.

The reason for this is that the bot uses the .jcheck/conf from the PR branch to find the fix version. The right thing to do would be to use the .jcheck/conf from the "merge branch", meaning the branch that would be pushed if the PR were integrated, which is the result of applying the patch from the PR branch on top of the then-current target branch. This is currently too expensive, so the source branch is used instead. While discussing this offline, I had asked whether the target branch could be used, but that runs into a worse problem where we wouldn't be able to integrate the start-of-release PR that bumps the JBS version and implements changes that require a CSR.