G201/G202: add checks for injection into sql.Conn methods

[imirkin]

We check sql.DB and sql.Tx, but sql.Conn appears to have been missed. It carries the same issues as DB/Tx in terms of injection.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.15%. Comparing base (1216c9b) to head (3b1b75f).
Report is 74 commits behind head on master.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1352      +/-   ##
==========================================
- Coverage   68.49%   63.15%   -5.35%     
==========================================
  Files          75       74       -1     
  Lines        4384     5179     +795     
==========================================
+ Hits         3003     3271     +268     
- Misses       1233     1780     +547     
+ Partials      148      128      -20     

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.