chore: Do not print any output when check-structfield-settings is OK

[alexandear]

This PR changes check-structcheck-settings to output nothing when structcheck settings are OK.

Before:

❯ ./script/generate.sh
/Users/alexandear/src/github.com/google/go-github/tools/metadata
/Users/alexandear/src/github.com/google/go-github/example
/Users/alexandear/src/github.com/google/go-github/example/newreposecretwithlibsodium
/Users/alexandear/src/github.com/google/go-github/otel
/Users/alexandear/src/github.com/google/go-github/scrape
/Users/alexandear/src/github.com/google/go-github/tools
/Users/alexandear/src/github.com/google/go-github/tools/check-structfield-settings
/Users/alexandear/src/github.com/google/go-github/tools/fmtpercentv
/Users/alexandear/src/github.com/google/go-github/tools/sliceofpointers
/Users/alexandear/src/github.com/google/go-github/tools/structfield
No obsolete structfield exceptions found.

After

❯ ./script/generate.sh
/Users/alexandear/src/github.com/google/go-github/tools/metadata
/Users/alexandear/src/github.com/google/go-github/example
/Users/alexandear/src/github.com/google/go-github/example/newreposecretwithlibsodium
/Users/alexandear/src/github.com/google/go-github/otel
/Users/alexandear/src/github.com/google/go-github/scrape
/Users/alexandear/src/github.com/google/go-github/tools
/Users/alexandear/src/github.com/google/go-github/tools/check-structfield-settings
/Users/alexandear/src/github.com/google/go-github/tools/fmtpercentv
/Users/alexandear/src/github.com/google/go-github/tools/sliceofpointers
/Users/alexandear/src/github.com/google/go-github/tools/structfield

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.52%. Comparing base (ab5ad47) to head (4a0f723).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4001   +/-   ##
=======================================
  Coverage   93.52%   93.52%           
=======================================
  Files         207      207           
  Lines       17597    17597           
=======================================
  Hits        16458    16458           
  Misses        938      938           
  Partials      201      201           

☔ 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.

[gmlewis]

Thank you, @alexandear!
LGTM.
Merging.