Fix CI build

[acroca]

We're having some build failure sin main: #978

[Copilot]

Pull request overview

This PR addresses CI build failures on main by tightening type information around protobuf Any.Is(...) checks in the gRPC helpers, likely resolving static type-checking failures introduced by recent dependency/stub changes.

Changes:

• Add cast and Descriptor imports for protobuf descriptor typing.
• Cast message.DESCRIPTOR to Descriptor when calling GrpcAny.Is(...) in unpack().

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.39%. Comparing base (bffb749) to head (69822b6).
⚠️ Report is 100 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #979      +/-   ##
==========================================
- Coverage   86.63%   80.39%   -6.24%     
==========================================
  Files          84      136      +52     
  Lines        4473    12590    +8117     
==========================================
+ Hits         3875    10122    +6247     
- Misses        598     2468    +1870     

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[sicoyle]

thank you!!