Remove getElementsByTagNameNS() for cases which can never find a element

[staabm]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.61%. Comparing base (d8bf935) to head (af65ff8).
⚠️ Report is 5 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1119      +/-   ##
============================================
- Coverage     88.63%   88.61%   -0.03%     
+ Complexity     1398     1396       -2     
============================================
  Files           105      105              
  Lines          4795     4785      -10     
============================================
- Hits           4250     4240      -10     
  Misses          545      545              

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

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[staabm]

we call this method on a document, which at this point of time cannot already contain a <tests> element.