Update GHA cache actions

[dyfer]

Purpose and Motivation

This is a maintenance PR, updating the cache action to the newest version.

install-qt-action was also updated and now features built-in caching, which is enabled instead of a separate caching action for downloaded qt.

I also added restore-keys to homebrew cache, so that the download cache will get updated daily, while still using cache from the previous day.

EDIT: qtwebengine was explicitly added to the Windows build matrix so that it can be disabled in the MinGW build. IIUC qtwebengine was never available for the 'win64_mingw81' architecture, but previous version of the install-qt-action would not check that and proceeded to install qt regardless.

Types of changes

• Housekeeping (?)

To-do list

• [x] Code is tested
• n/a All tests are passing
• n/a Updated documentation
• [x] This PR is ready for review