[ATR-24112] Use proper setup of TDT via python in the used-by-ART-test testAthenaTrigAOD_TrigDecTool.py

Default-instantiation of the TDT is not leaving jobs in a good state. See ATR-24112 where the config is mangled.

This looks to have been exacerbated by switching the default behavior to using the (thread-safe) config service in place of the unsafe config tool.

Moves this test to use the correct TDT setup.

There are more instances of similar the code base - will open a ticket for these.