Provide CI support for prt-mp7-02 and prt-mp7-04

[jlarsen-usgs]

Current CI excludes these two problems in conftest.py due to issues with modflow6-examples for these two problems in CI. Please see GH Action #709, Windows testing for modflow6 example problems for more details.

[wpbonelli]

These are backwards tracking models. The issue is that the examples currently use flopy to reverse head/budget files in between the flow and particle tracking model runs. Once we have native backwards tracking in PRT these will work.