fix(types): Add cast for HybridCloudForeignKey in test fixture

[JoshFerge]

Summary

Add isinstance check and cast to narrow the generic type parameters for HybridCloudForeignKey fixture return type.

Changes

• Add isinstance check for HybridCloudForeignKey
• Use cast() to narrow generic type parameters to [int, int]
• Ensures type safety in test fixture

Test plan

• Existing tests pass
• Mypy type checking passes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #103027      +/-   ##
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- Coverage   80.75%    80.64%   -0.11%     
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  Files        9145      9140       -5     
  Lines      395020    392793    -2227     
  Branches    24968     24968              
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- Hits       319002    316777    -2225     
+ Misses      75617     75615       -2     
  Partials      401       401