fix(cmake): client libraries link to shared proto deps

[dbolduc]

Part of the work for #8022

Client libraries link against shared proto libraries they depend on.

• GCB: https://console.cloud.google.com/cloud-build/builds;region=us-east1/286f07b1-a795-431c-a12a-8686219ae2fc;tab=detail?project=cloud-cpp-testing-resources
• Raw: https://storage.googleapis.com/cloud-cpp-community-publiclogs/logs/google-cloud-cpp/12506/67da268e17e70c150cf74757df90c6d4f9b7740a/fedora-37-cxx20-cxx20/log-286f07b1-a795-431c-a12a-8686219ae2fc.txt

---

This change is 

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01% ⚠️

Comparison is base (bcbc8d4) 93.63% compared to head (ba8b5d5) 93.62%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12514      +/-   ##
==========================================
- Coverage   93.63%   93.62%   -0.01%     
==========================================
  Files        2043     2043              
  Lines      180935   180935              
==========================================
- Hits       169413   169408       -5     
- Misses      11522    11527       +5     

see 5 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.