Fix tests for Python 3.14

[jtpio]

As noticed in #627, tests fail with Python 3.14:

https://github.com/jupyter-server/jupyter_releaser/actions/runs/20077023551/job/57594034835?pr=627

=========================== short test summary info ===========================
ERROR tests/test_cli.py::test_delete_release - pytest.PytestUnraisableExceptionWarning: Exception ignored while calling deallocator <function _TemporaryFileCloser.__del__ at 0x0000027F03BB5900>: None
FAILED tests/test_cli.py::test_build_changelog - subprocess.CalledProcessError: Command '['C:/Users/runneradmin/AppData/Local/hatch/env/virtual/jupyter-releaser/U0jvGu-K/cov/Scripts/pre-commit.EXE', 'run', '-a']' returned non-zero exit status 1.
FAILED tests/test_cli.py::test_build_changelog_existing - subprocess.CalledProcessError: Command '['C:/Users/runneradmin/AppData/Local/hatch/env/virtual/jupyter-releaser/U0jvGu-K/cov/Scripts/pre-commit.EXE', 'run', '-a']' returned non-zero exit status 1.
FAILED tests/test_cli.py::test_build_changelog_backport - subprocess.CalledProcessError: Command '['C:/Users/runneradmin/AppData/Local/hatch/env/virtual/jupyter-releaser/U0jvGu-K/cov/Scripts/pre-commit.EXE', 'run', '-a']' returned non-zero exit status 1.
FAILED tests/test_cli.py::test_build_changelog_slashes - subprocess.CalledProcessError: Command '['C:/Users/runneradmin/AppData/Local/hatch/env/virtual/jupyter-releaser/U0jvGu-K/cov/Scripts/pre-commit.EXE', 'run', '-a']' returned non-zero exit status 1.
============== 4 failed, 1 passed, 2 warnings, 1 error in 48.52s ==============

[jtpio]

So for now #627 sticks to 3.13, but we should look into testing on 3.14 soon after and fix those tests.