test: add missing test for empty string in path.posix.normalize()

[cruzz77]

Refs: #60822

Problem

The implementation of path.posix.normalize() explicitly handles the empty string case:

if (path.length === 0)
  return '.';

However, the test suite (test/parallel/test-path-normalize.js) did not include a test for this behavior, leaving this branch untested.

Fix

This PR adds the following assertion to ensure the empty path case is properly covered:

assert.strictEqual(path.posix.normalize(''), '.');

• Improves test coverage for the path subsystem
• Ensures edge-case behavior is tested and protected
• Helps prevent regressions during future refactors

Tests

• ✔ Added new test case
• ✔ All existing tests pass

[nodejs-github-bot]

Review requested:

• @nodejs/path

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.53%. Comparing base (1758b74) to head (77e97e2).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #60823      +/-   ##
==========================================
- Coverage   88.56%   88.53%   -0.03%     
==========================================
  Files         703      703              
  Lines      208268   208268              
  Branches    40175    40171       -4     
==========================================
- Hits       184444   184394      -50     
- Misses      15828    15874      +46     
- Partials     7996     8000       +4     

see 31 files with indirect coverage changes

🚀 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.

[aduh95]

That's already covered by the tests

node/test/parallel/test-path-zero-length-strings.js

Lines 22 to 23 in 7fe8085

	// Normalize will return '.' if the input is a zero-length string
	assert.strictEqual(path.posix.normalize(''), '.');

[cruzz77]

Thank you for pointing that out and for taking the time to review my PR. I totally understand why the PR was closed since this case is already properly tested.
I'm still learning about the codebase and appreciate the guidance. Thank you for your support!