tests: hopefully fix `test-doctest.py` on Windows and more 1. Shell syntax understood by `shell=True` depends on the platform. Instead, pass `shell=False` and call `sh` explicitly to interpret the command correctly. 2. Stop setting `HGRCPATH=/dev/null`, so the setting `experimental.evolution=createmarkers` is set correctly. The reason I set HGRCPATH to /dev/null previously is because of misunderstanding where I thought the Python script had no HGRC to edit. As it turns out, there is in fact a valid temporary HGRC pointed to by HGRCPATH in this context so we don't seem to need this. /shrug