Set COVERAGE_PROCESS_START correctly
Set COVERAGE_PROCESS_START correctly

Contrary to the documentation, setting COVERAGE_PROCESS_START is not
enough but it should be a path to a valid configuration file.

https://coverage.readthedocs.io/en/6.2/subprocess.html
> It examines the COVERAGE_PROCESS_START environment variable, and if it
is set, begins coverage measurement.

https://github.com/nedbat/coveragepy/blob/c9d821deba6f7ee5eef30fef5355f7c93808b4f9/coverage/control.py#L1147
```
cps = os.environ.get("COVERAGE_PROCESS_START")
if not cps:
    # No request for coverage, nothing to do.
    return None
```

manicmaniac/backquotes