test_runner: require --enable-source-maps for source map coverage

[RedYetiDev]

Ref: #54753 (comment) (CC @MoLow @cjihrig)

Coverage is currently an experimental feature, so this is non-breaking, right?

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.24%. Comparing base (8b8fc53) to head (a478463).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/test_runner/coverage.js	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #55039   +/-   ##
=======================================
  Coverage   88.23%   88.24%           
=======================================
  Files         652      652           
  Lines      183855   183856    +1     
  Branches    35856    35855    -1     
=======================================
+ Hits       162227   162240   +13     
+ Misses      14909    14900    -9     
+ Partials     6719     6716    -3     

Files with missing lines	Coverage Δ
lib/internal/test_runner/coverage.js	64.67% <50.00%> (-0.10%)	⬇️

... and 22 files with indirect coverage changes