Add more unit tests for GRPCRoute

[sjberman]

Problem: The change_processor tests were missing GRPCRoute cases.

Solution: Add these test cases to improve coverage of GRPCRoutes.

Closes #2352

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

Release notes

If this PR introduces a change that affects users and needs to be mentioned in the release notes,
please add a brief note that summarizes the change.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.86%. Comparing base (f56f525) to head (3a8a514).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2835   +/-   ##
=======================================
  Coverage   89.86%   89.86%           
=======================================
  Files         107      107           
  Lines       10997    10997           
  Branches       50       50           
=======================================
  Hits         9883     9883           
  Misses       1054     1054           
  Partials       60       60           

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[kate-osborn]

🚀