fix(generator): correct doxygen comments

[coryan]

Before:

After:

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This change is 

[codecov]

Codecov Report

Base: 93.97% // Head: 93.97% // No change to project coverage 👍

Coverage data is based on head (a004299) compared to base (97de9fc).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10500   +/-   ##
=======================================
  Coverage   93.97%   93.97%           
=======================================
  Files        1626     1626           
  Lines      146836   146836           
=======================================
  Hits       137991   137991           
  Misses       8845     8845           

Impacted Files	Coverage Δ
...ation_tests/golden/v1/golden_kitchen_sink_client.h	100.00% <ø> (ø)
...ration_tests/golden/v1/golden_thing_admin_client.h	100.00% <ø> (ø)
generator/internal/client_generator.cc	26.94% <ø> (ø)
google/cloud/internal/async_connection_ready.cc	89.36% <0.00%> (-4.26%)	⬇️
...le/cloud/storage/internal/curl_download_request.cc	89.63% <0.00%> (+0.33%)	⬆️
...integration_tests/schema_admin_integration_test.cc	100.00% <0.00%> (+1.11%)	⬆️

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