fix: Enable subprocess coverage (#289)

The default CLI test in new projects runs `__main__.py` in a subprocess,
until pytest-cov 7.0.0 subprocesses were automatically included in
coverage but that has now changed and we must explicitly enable it in
order to avoid sudden unexpected drops in code coverage.

See docs:
https://pytest-cov.readthedocs.io/en/latest/subprocess-support.html

Author: callumforrester

template/pyproject.toml.jinja

@@ -71,6 +71,7 @@ filterwarnings = "error"
 testpaths = "docs src tests"
 
 [tool.coverage.run]
+patch = ["subprocess"]
 data_file = "/tmp/{{ package_name }}.coverage"
 
 [tool.coverage.paths]