grpc: fixing typos

[mbissa]

This change fixes some typos.
RELEASE NOTES: none

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.32%. Comparing base (a2a2023) to head (f6ff2e8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8796      +/-   ##
==========================================
- Coverage   83.32%   83.32%   -0.01%     
==========================================
  Files         418      418              
  Lines       32897    32897              
==========================================
- Hits        27413    27410       -3     
- Misses       4085     4089       +4     
+ Partials     1399     1398       -1     

Files with missing lines	Coverage Δ
internal/stats/metrics_recorder_list.go	80.00% <ø> (ø)
internal/xds/xdsdepmgr/xds_dependency_manager.go	80.87% <ø> (ø)

... and 19 files with indirect coverage changes

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