jenkins: lots of space used by aqa-tests clones in @script directories on `workspace` file system

_Split out from #4025 which was a critical out of space condition to be able to progress the underlying issue. Some discussion was in a [slack thread](https://adoptium.slack.com/archives/C53GHCXL4/p1755172487793659?thread_ts=1755170899.843479&cid=C53GHCXL4) in August 14th_

We need to look at whether we can reduce the amount of space that is being used in the workspace directory on the jenkins server. Each Test job (of which there are thousands) has a `@script` variant which contains a full copy (Just short of 300MiB) of the `aqa-tests` repository.

We need to understand why this is being left around and see whether we can prevent it.

jenkins is leaving around a load of 287MiB @script directories for a lot of jobs (certainly all the test ones that I can see) e.g.
```
287M Test_openjdk24_hs_special.system_x86-64_windows@script
287M Test_openjdk24_hs_special.system_x86-64_windows_rerun@script
287M Test_openjdk24_hs_special.system_x86-64_windows_testList_0@script
287M Test_openjdk24_hs_special.system_x86-64_windows_testList_1@script
287M Test_openjdk25_hs_special.system_x86-64_linux@scriptls
```
There are 1423 of those for jdk26 already (Pattern: Test*26*script ) by the look of it which will probably be chewing up over 300GiB in total

Start by inspecting the Jenkins workspace and the Test*26* @script directories, then trace how each job leaves a full aqa-tests repository copy behind. Use the examples and the 1423-directory count as the baseline. Done means the cause is documented and the workspace no longer accumulates unnecessary copies without disrupting test jobs.

Written by the indexing model from the issue text.