PyUtils: Go back to using regex for reading the number of entries in AthFileLite

This reverts !69921 (merged) and goes back to what I originally implemented in !67863 (merged) but uses the APRDefaults in the regex for the collection names. It looks like the former broke a unit-test where we were reading an ESD from 2011, which has POOLContainer_DataHeader instead of POOLContainer for the DataHeader.

Closes ATEAM-968

cc: @gemmeren

added full-integration-tests full-unit-tests labels

This merge request affects 1 package:

• Tools/PyUtils

This merge request affects 1 file:

• Tools/PyUtils/python/AthFileLite.py

added Tools analysis-review-required main review-pending-level-1 labels

removed review-pending-level-1 label

added review-approved label

enabled an automatic merge when the pipeline for 6d91eec7 succeeds

CI Result SUCCESS (hash 6d91eec7)

	Athena	AthSimulation	AthGeneration	AnalysisBase	AthAnalysis
externals
cmake
make
tests

Full details available on this CI monitor view. Check the JIRA CI status board for known problems
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
AthAnalysis: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-EL9 6790] (remote access info)

merged

mentioned in commit 978969f1