feat: add post austria

[firstof9]

Proposed change

Add Post Austria to supported shippers.

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 fixes or closes issue: fixes [Feature Request] Adding Post Austria #1007

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.25%. Comparing base (8608d22) to head (09fc0ae).
Report is 50 commits behind head on dev.

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1008      +/-   ##
==========================================
- Coverage   95.07%   93.25%   -1.82%     
==========================================
  Files           8        8              
  Lines        1482     1616     +134     
==========================================
+ Hits         1409     1507      +98     
- Misses         73      109      +36     

Files with missing lines	Coverage Δ
custom_components/mail_and_packages/const.py	100.00% <ø> (ø)

... and 3 files with indirect coverage changes