Updated the open AQ filter to ensure PM values for ppm are filtered out

[rstrange-scottlogic]

Also includes a small refactoring of the open_aq_adapter tests to mock the same way others do

[github-actions[bot]]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
781	734	94%	80%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
air-quality-backend/src/air_quality/etl/in_situ/openaq_adapter.py	98%	🟢
TOTAL	98%	🟢

updated for commit: 7f3f080 by action🐍