[8.0] fix: AREX submission issue

[aldbr]

The submission error response is either a dict or a list, it seems to be random:

• [{'status-code': '500', 'reason': '...'}] <class 'list'>
• {'status-code': '500', 'reason': '...'} <class 'dict'>

BEGINRELEASENOTES *Resources FIX: AREX submission issue not properly handled ENDRELEASENOTES

[DIRACGridBot]

Sweep summary

Sweep ran in https://github.com/DIRACGrid/DIRAC/actions/runs/9711231452

Successful:

• integration