Fix a link in developing.rst and update context with Pytest

Moore MR pipeline (build docs) contain, among others, two errors:

/builds/lhcb/Moore/doc/tutorials/developing.rst:81: ERROR: Indirect hyperlink target "gaudi"  refers to target "gaudipolicy", which does not exist.
/builds/lhcb/Moore/doc/tutorials/developing.rst:81: ERROR: Unknown target name: "gaudipolicy".

This MR fixes them by repairing the broken link in the docs. It also updates the information where the source code for the QMTest and Pytest can be found.