fix(types): Add None check for projectId in installation external requests

[JoshFerge]

Summary

Validate projectId before querying to handle the case where it's not provided in the request.

Changes

• Extract project_id from request.GET
• Add None check before querying Project model
• Set project to None if projectId is missing or project doesn't exist

Test plan

• Existing tests pass
• Mypy type checking passes

[codecov]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...ps/api/endpoints/installation_external_requests.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #103024      +/-   ##
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- Coverage   80.75%    80.64%   -0.11%     
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  Files        9145      9140       -5     
  Lines      395020    392796    -2224     
  Branches    24968     24968              
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- Hits       319002    316777    -2225     
- Misses      75617     75618       +1     
  Partials      401       401