Some tests depend on execution order and inherited color environment variables

Describe the bug

Hej, I found some Sphinx tests that are flaky because they depend on shared test directories or environment variables inherited from the test runner.

test_missing_reference_conditional_pending_xref shares its source and build directory with Python domain tests. Depending on test order, it can leave generated output that causes test_python_python_use_unqualified_type_names to reuse stale build data.

The status iterator tests force color with FORCE_COLOR=1, but do not clear NO_COLOR or NO_COLOUR. If either variable is set in the environment, NO_COLOR takes precedence and the tests can receive newline-based output instead of the expected carriage-return output.

How to Reproduce

For the test-order issue, run:

uv run pytest -q --tb=short \
  tests/test_transforms/test_transforms_post_transforms.py::test_missing_reference_conditional_pending_xref \
  tests/test_domains/test_domain_py.py::test_python_python_use_unqualified_type_names

The second test can fail because the existing HTML output is considered up-to-date and is not regenerated. For the environment-variable issue, run:

NO_COLOR=1 uv run pytest -q --tb=short \
  tests/test_util/test_util_display.py::test_status_iterator_verbosity_0

The test expects output containing \r, but receives output containing \n instead. NO_COLOUR=1 has the same effect.

Environment Information

Platform:              linux; (Linux-6.18.33.2-microsoft-standard-WSL2-x86_64-with-glibc2.39)
Python version:        3.14.7 (main, Aug 14 2026, 15:35:28) [Clang 22.1.3 ])
Python implementation: CPython
Sphinx version:        9.1.1+/f4bca342e
Docutils version:      0.22.3
Jinja2 version:        3.1.6
Pygments version:      2.19.2

Sphinx extensions

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Additional context

The affected tests are:

• tests/test_transforms/test_transforms_post_transforms.py::test_missing_reference_conditional_pending_xref
• tests/test_domains/test_domain_py.py::test_python_python_use_unqualified_type_names
• tests/test_util/test_util_display.py::test_status_iterator_verbosity_0
• tests/test_util/test_util_display.py::test_status_iterator_verbosity_1