debian/rules: Specify Go packages to build

[adombeck]

Fixes the build of the Debian package to fail with:

dh_missing: warning: usr/bin/docgen exists in debian/tmp but is not installed to anywhere
dh_missing: error: missing files, aborting

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.99%. Comparing base (f40fcbe) to head (cd88387).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1264      +/-   ##
==========================================
- Coverage   86.04%   85.99%   -0.05%     
==========================================
  Files          99       99              
  Lines        6685     6685              
  Branches      111      111              
==========================================
- Hits         5752     5749       -3     
- Misses        877      880       +3     
  Partials       56       56              

☔ 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.