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

[sxa]

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 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: Test26script ) by the look of it which will probably be chewing up over 300GiB in total