trapme: alternate aqa-tests branches cause failure except on Grinder jobs

[sxa]

Running using a custom ADOPTOPENJDK_REPO and ADOPTOPENJDK_BRANCH results in failures on the main test jobs, although not on Grinders. This used to work but now gives a rather cryptic error message to the user:

hudson.plugins.git.GitException: Command "git fetch --tags --force --progress --prune -- origin +refs/heads/refine_concurrency_logic:refs/remotes/origin/refine_concurrency_logic" returned status code 128:
stdout: 
stderr: fatal: couldn't find remote ref refs/heads/refine_concurrency_logic

It seems likely that this changes as a result of Likely started when https://github.com/adoptium/aqa-tests/pull/5204 was merged. I, and other temurin committers (slack thread 1, slack thread 2, ) have tripped over this, so if we plan to keep this behavior and leave the parameter on the jobs we should aim to give some sort of warning to the user under these circumstances to give them a pointer as to why it has happened and how to resolve it.