refactor: stop setting sensors unavailable if IMAP polling fails

[firstof9]

Proposed change

Stop setting sensors unavailable when IMAP polling fails.

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: n/a

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.90%. Comparing base (8608d22) to head (a72c269).
Report is 59 commits behind head on dev.

Files with missing lines	Patch %	Lines
custom_components/mail_and_packages/__init__.py	66.66%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1039      +/-   ##
==========================================
- Coverage   95.07%   92.90%   -2.17%     
==========================================
  Files           8        9       +1     
  Lines        1482     1649     +167     
==========================================
+ Hits         1409     1532     +123     
- Misses         73      117      +44     

Files with missing lines	Coverage Δ
...stom_components/mail_and_packages/binary_sensor.py	100.00% <ø> (+2.81%)	⬆️
custom_components/mail_and_packages/camera.py	92.52% <ø> (+3.63%)	⬆️
custom_components/mail_and_packages/const.py	100.00% <100.00%> (ø)
custom_components/mail_and_packages/sensor.py	92.50% <ø> (-0.13%)	⬇️
custom_components/mail_and_packages/__init__.py	84.67% <66.66%> (-7.44%)	⬇️

... and 2 files with indirect coverage changes