fix(test): EncodingWarning: 'encoding' argument not specified

[even-even]

Thanks for contributing, make sure you address all the checklists (for details on how see development documentation)

• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation

Hello

When running the tests, I see warnings.
`(virtualenv) ➜ virtualenv git:(main) tox -e py315
...
...
....................s............................................................................................ss...sss......................ss...... [ 41%]
s.....s....s....................s.....s...............s.s..s.......................................................................................s... [ 83%]
......................s............s........s............. [100%]
====================================================================== warnings summary =======================================================================
tests/unit/test_util.py::test_safe_delete_raises_the_original_error_not_a_retry_failure
/Users/vyuroshchin/github_my/virtualenv/tests/unit/test_util.py:64: EncodingWarning: 'encoding' argument not specified
(blocked / "wheel.py").write_text("cached")

tests/unit/test_util.py::test_safe_delete_keeps_the_other_mode_bits_when_clearing_read_only
/Users/vyuroshchin/github_my/virtualenv/tests/unit/test_util.py:79: EncodingWarning: 'encoding' argument not specified
blocked.write_text("cached")

tests/unit/seed/embed/test_bootstrap_link_via_app_data.py::test_safe_extract_zip_allows_normal_entry
/Users/vyuroshchin/github_my/virtualenv/tests/unit/seed/embed/test_bootstrap_link_via_app_data.py:272: EncodingWarning: 'encoding' argument not specified
assert (target / "pkg" / "inner.txt").read_text() == "payload"

tests/unit/test_util.py::test_safe_delete_removes_read_only_files
/Users/vyuroshchin/github_my/virtualenv/tests/unit/test_util.py:36: EncodingWarning: 'encoding' argument not specified
marked.write_text("cached")

tests/unit/test_util.py::TestCacheDirMigration::test_migrate_old_to_new
/Users/vyuroshchin/github_my/virtualenv/tests/unit/test_util.py:128: EncodingWarning: 'encoding' argument not specified
(tmp_path / "old-data" / "test.txt").write_text("hello")

tests/unit/test_util.py::TestCacheDirMigration::test_migrate_old_to_new
/Users/vyuroshchin/github_my/virtualenv/tests/unit/test_util.py:137: EncodingWarning: 'encoding' argument not specified
assert (tmp_path / "new-cache" / "test.txt").read_text() == "hello"

tests/unit/test_util.py::TestCacheDirMigration::test_symlink_app_data_survives_migration[False]
tests/unit/test_util.py::TestCacheDirMigration::test_symlink_app_data_survives_migration[True]
/Users/vyuroshchin/github_my/virtualenv/tests/unit/test_util.py:202: EncodingWarning: 'encoding' argument not specified
(wheel_img / "pip.dist-info" / "METADATA").write_text("Name: pip")

tests/unit/test_util.py::TestCacheDirMigration::test_no_migration_when_new_exists
/Users/vyuroshchin/github_my/virtualenv/tests/unit/test_util.py:155: EncodingWarning: 'encoding' argument not specified
(tmp_path / "old-data" / "old.txt").write_text("old")

tests/unit/activation/test_bash.py::test_bash_activate_relocation_resolves_virtual_env
/Users/vyuroshchin/github_my/virtualenv/tests/unit/activation/test_bash.py:96: EncodingWarning: 'encoding' argument not specified.
result = subprocess.run(

tests/unit/create/test_creator.py::test_pyenv_cfg_preserves_symlinks
/Users/vyuroshchin/github_my/virtualenv/tests/unit/create/test_creator.py:827: EncodingWarning: 'encoding' argument not specified
real_file.write_text("test")

tests/unit/create/test_creator.py::test_pyenv_cfg_preserves_symlinks
/Users/vyuroshchin/github_my/virtualenv/tests/unit/create/test_creator.py:842: EncodingWarning: 'encoding' argument not specified
written_content = cfg_path.read_text()

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
-------------------------------------- generated xml file: /Users/vyuroshchin/github_my/virtualenv/.tox/junit.py315.xml ---------------------------------------
======================================================== 340 passed, 20 skipped, 12 warnings in 46.79s ========================================================
`

In PR I fixed this warnings like https://github.com/python-poetry/poetry/pull/8893/changes#diff-a1176a239bb3b9e9eb632f8f1090097a3630cea9f405da6b0506642e5343dd07R921 (add param encoding="utf-8" in tests)