CI: Use -j1 for python-dev build to avoid flaky build error
xref #47305

e.g. https://github.com/pandas-dev/pandas/runs/8280474438?check_suite_focus=true

Thanks @datapythonista. I think the closest explanation of the issue can be found in https://github.com/pandas-dev/pandas/pull/47310#issuecomment-1232024906