fix(common): missing Abseil deps in pkgconfig

[coryan]

This change is 

[codecov]

Codecov Report

Base: 94.03% // Head: 94.03% // No change to project coverage 👍

Coverage data is based on head (f2d55b2) compared to base (423bfc6).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #10616   +/-   ##
=======================================
  Coverage   94.03%   94.03%           
=======================================
  Files        1669     1669           
  Lines      149593   149593           
=======================================
  Hits       140664   140664           
  Misses       8929     8929           

Impacted Files	Coverage Δ
google/cloud/internal/async_rpc_details.h	95.00% <0.00%> (-5.00%)	⬇️
...integration_tests/schema_admin_integration_test.cc	98.88% <0.00%> (-1.12%)	⬇️
...ud/spanner/integration_tests/client_stress_test.cc	84.21% <0.00%> (-0.66%)	⬇️
...torage/examples/storage_service_account_samples.cc	97.63% <0.00%> (-0.60%)	⬇️
google/cloud/pubsub/samples/samples.cc	87.99% <0.00%> (+0.07%)	⬆️
...cloud/pubsub/internal/subscription_session_test.cc	98.49% <0.00%> (+0.33%)	⬆️
...le/cloud/storage/internal/curl_download_request.cc	89.63% <0.00%> (+0.33%)	⬆️

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