Include the external/ folder in the coverage report for gulp unittestcli

[Snuffleupagus]

Given that the (browser) gulp unittest coverage includes the external/ folder, it seems reasonable to include that folder in the coverage report when running unit-tests in Node.js as well.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.92%. Comparing base (ac51bdf) to head (d33d9fc).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21226      +/-   ##
==========================================
- Coverage   55.92%   55.92%   -0.01%     
==========================================
  Files         220      220              
  Lines       58990    58990              
==========================================
- Hits        32993    32992       -1     
- Misses      25997    25998       +1     

Flag	Coverage Δ
fonttest	8.65% <ø> (ø)
unittest	55.19% <ø> (-0.01%)	⬇️
unittestcli	54.44% <ø> (-1.26%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

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

[calixteman]

We don't use c8 anymore so you can remove the json.

[timvandermeij]

Looks good to me like this; thanks!