Fixing config parser for bright limit

[astronomerritt]

Fixes #1022.

Desired behaviour:

• if the bright limit keyword is not in the config file (e.g. if you are using Rubin_known_object_prediction.ini) the bright limit cut should be skipped

Actual behaviour:

• code broke completely because I forgot to wrap some stuff in an if-statement in PPConfigParser

Fix:

• put the if-statement in

Review Checklist for Source Code Changes

• [x] Does pip install still work?
• [x] Have you written a unit test for any new functions?
• [x] Do all the units tests run successfully?
• [x] Does Sorcha run successfully on a test set of input files/databases?
• [x] Have you used black on the files you have updated to confirm python programming style guide enforcement?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 41.66667% with 7 lines in your changes missing coverage. Please review.

Project coverage is 81.04%. Comparing base (c2b800c) to head (8ab8dbf). Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
src/sorcha/modules/PPConfigParser.py	41.66%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1024 +/- ## ========================================== + Coverage 80.90% 81.04% +0.13% ========================================== Files 70 70 Lines 3148 3149 +1 ========================================== + Hits 2547 2552 +5 + Misses 601 597 -4 ```

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[astronomerritt]

Please ignore CodeCov, PPConfigParser is impossible to unit test properly in its current form. (One day I'll fix it. ONE DAY.)