ci: Fix borked Python environment on macOS
ci: Fix borked Python environment on macOS

It looks like multiple Python3 environments are installed and running
pip3 attempts to run a non-existent python3 binary. The recommended
workaround is to invoke pip as a python module.

Change-Id: I0bf2e47fa11b3c1014706960f5a34a85f64fa166
Reviewed-by: Ivan Komissarov <96f14e4d07227e958f51f7d2898113639e9498d9@gmail.com>
Reviewed-by: Richard Weickelt <320bca71fc381a4a025636043ca86e734e31cf8b@weickelt.de>

qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs