fix windows release with Qt6. (#748)

fix windows release with Qt6. (#748)

* fix windows release with Qt6.

windeployqt failed to deploy Qt6Core5Compat.dll because it was
not used by the gui and we didn't tell windeployqt there was
another executable to scan for dependencies.

* fiddle with github cache conditionals.

cache was restored, but we tried to install qt anyway.

* Revert "fiddle with github cache conditionals."

This reverts commit fece79e5e56de2f957960236bb851c6bc7682d7c.

* try to get github action conditionals working again.

* Revert "try to get github action conditionals working again."

This reverts commit 3152108e5267580f3836b9f6aadc7dfa2ecfe347.

* work around apparent bug in github action conditonal processing.

* the second half of the workaround

* fool around with bash

* more bash foolishness.