test: fix case-insensitive path matching on Windows

[mcollina]

Summary

Fixes flaky test-node-output-sourcemaps test on Windows CI.

Problem

On Windows, file paths are case-insensitive but JavaScript string comparison is case-sensitive. When the drive letter case differs between the computed project root (e.g., C:/workspace/...) and the actual output from child processes (e.g., c:/workspace/...), the path replacement in transformProjectRoot() would fail.

This causes snapshot tests to fail with errors like:

Expected values to be strictly equal
actual: 'c:/workspace/node-test-binary.../test/fixtures/...'
expected: '<project-root>/test/fixtures/...'

Solution

Use case-insensitive regex replacement (gi flag) on Windows to ensure paths are correctly normalized regardless of drive letter casing.

Verification

Tested locally with python3 tools/test.py --repeat 20 test/parallel/test-node-output-sourcemaps.mjs - all passed.

Refs: nodejs/reliability#1453

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.76%. Comparing base (8c32389) to head (08d1976).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61682      +/-   ##
==========================================
+ Coverage   89.75%   89.76%   +0.01%     
==========================================
  Files         674      674              
  Lines      204394   204394              
  Branches    39278    39274       -4     
==========================================
+ Hits       183448   183482      +34     
+ Misses      13238    13232       -6     
+ Partials     7708     7680      -28     

see 31 files with indirect coverage changes

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