fix: fix small bug when enabling usps mail delivered sensor

[firstof9]

Proposed change

Fix small bug when enabling usps mail delivered sensor and add test email

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (which adds functionality)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests
• Documentation update
• Adds a new shipper
• Update existing shipper

Additional information

• This PR is related to issue: Add Sensor for delivered USPS mail. #915

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.56%. Comparing base (8608d22) to head (01b7e3d).
Report is 30 commits behind head on dev.

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #958      +/-   ##
==========================================
- Coverage   95.07%   93.56%   -1.52%     
==========================================
  Files           8        8              
  Lines        1482     1569      +87     
==========================================
+ Hits         1409     1468      +59     
- Misses         73      101      +28     

Files	Coverage Δ
...stom_components/mail_and_packages/binary_sensor.py	97.29% <100.00%> (+0.11%)	⬆️
custom_components/mail_and_packages/sensor.py	92.68% <100.00%> (+0.05%)	⬆️

... and 4 files with indirect coverage changes