Split out pre command

Co-authored-by: Bernát Gábor <[email protected]>

tox.ini

@@ -33,9 +33,8 @@ install_command = python -Im pip install --no-compile {opts} {packages}
 set_env =
  COVERAGE_PROCESS_START={toxinidir}/pyproject.toml
  PYTHONWARNINGS=d
-commands =
- python -c 'f = open("{env_site_packages_dir}/cov.pth", "w"); f.write("import coverage; coverage.process_startup()"); f.close()'
- coverage run -m pytest {posargs:-n auto}
+commands_pre = python -c 'import pathlib; pathlib.Path("{env_site_packages_dir}/cov.pth").write_text("import coverage; coverage.process_startup()")'
+commands = coverage run -m pytest {posargs:-n auto}
 
 
 [testenv:coverage-report]