Mutate the EDM list in the test first, before it is imported into any other modules as a side-effect of further imports below. Temporary fix, we shouldn't be mutating variables in other modules like this.
Fixes PEBDSTest.py, closes [ ATR-28731]
Bug arose as a side-effect of !68370 changing the order of python imports, this test and some other code is unfortunately sensitive to this - general follow up on this class of bugs at [ ATR-28536]