test: move watch-iterator test to sequential

[gurgunday]

It's flaky, and this should fix it

This test calls tmpdir.refresh(). In the parallel suite, another test could be using that directory at the same time, so refresh causes cross-test interference

Beyond tmpdir, fs.watch tests are sensitive to system load and timing - it already relies on timeouts

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.45%. Comparing base (cff138c) to head (9514cf1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #60041      +/-   ##
==========================================
- Coverage   88.45%   88.45%   -0.01%     
==========================================
  Files         703      703              
  Lines      207546   207546              
  Branches    40016    40023       +7     
==========================================
- Hits       183595   183583      -12     
+ Misses      15956    15951       -5     
- Partials     7995     8012      +17     

see 39 files with indirect coverage changes

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[lpinca]

This test calls tmpdir.refresh(). In the parallel suite, another test could be using that directory at the same time, so refresh causes cross-test interference

This is not a valid reason. tmpdir.refresh() was designed for parallel execution.

Beyond tmpdir, fs.watch tests are sensitive to system load and timing - it already relies on timeouts

This is also not valid reason. There are other fs.watch tests like this (with timers) and they are not flaky. I did not investigate but it seems the issue is on macOS so it might be related to libuv/libuv#4503. See also https://github.com/nodejs/node/pull/54498/files.

cc: @pipobscure

[gurgunday]

Closing, created #60051