utils_test.popen: allow avoiding path modification, use sysconfig for portability

[jameslamb]

Closes #5069

Small updates to utils_test.popen():

• uses sysconfig.get_path("scripts") to handle differences across operating systems
• allows avoiding path modifications by passing an absolute path (e.g. popen(["/usr/local/bin/dask"]))

Notes for Reviewers

• Tests added / passed
• Passes pre-commit run --all-files

How I tested this

Locally, on my arm64 Mac

conda env create \
  --yes \
  --name distributed-dev \
  --file ./continuous_integration/environment-3.13.yaml

source activate distributed-dev
pip install --no-deps .
python -m pytest distributed \
  -m "not avoid_ci" \
  --leaks=fds

# === 10 failed, 3699 passed, 299 skipped, 7 deselected, 26 xfailed, 11 xpassed in 932.88s (0:15:32)

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

    27 files  ± 0      27 suites  ±0   9h 58m 25s ⏱️ - 4m 55s
 4 113 tests + 1   4 003 ✅  - 3    104 💤 ±0   6 ❌ + 4 
51 529 runs  +13  49 330 ✅ ±0  2 184 💤 ±0  15 ❌ +13 

For more details on these failures, see this check.

Results for commit 36dc532. ± Comparison against base commit 5da04d0.

[jacobtomlinson]

Thanks James! Overall I'm +1 on this change.

There are some failures on Windows that seem related though

FAILED distributed/cli/tests/test_dask_worker.py::test_dashboard_non_standard_ports - FileNotFoundError: Could not find 'C:\Users\runneradmin\miniconda3\envs\dask-distributed\Scripts\dask'. To avoid this warning, provide an absolute path to an existing installation to popen().
FAILED distributed/cli/tests/test_dask_worker.py::test_single_executable_works - FileNotFoundError: Could not find 'C:\Users\runneradmin\miniconda3\envs\dask-distributed\Scripts\dask-worker'. To avoid this warning, provide an absolute path to an existing installation to popen().
FAILED distributed/tests/test_utils_test.py::test_popen_file_not_found - Failed: Invalid regex pattern provided to 'match': incomplete escape \U at position 18