Qt 5.15 will be EOL on May 26 so we should start switching away from it.
We already have issues with many of the previous versions and qmake on
legacy distros so we should cut that off.
I will add a Qt6 release build for Windows in another PR so it can be
tested. We should switch to it as the delivered build after the next
release and stop using Qt5 altogether in the CI in the release
afterwards (that would get rid of several build steps). We could leave
it so you could still try to build it but no longer support it so it is
up to the user to get it to work before removing it completely later on.
* updated workflows to `jurplel/install-qt-action@v3`
* release-windows.yml: removed installation of unavailable `qthelp` module
* release-windows.yml: do not hard-code `tools_openssl_x64` version
* modernized some CMake invocations
* CI-unixish.yml: use `ccache` for Linux gcc CMake builds
* CI-unixish-docker.yml: use `ccache` for Linux gcc CMake builds
* CI-unixish-docker.yml: enabled CMake build with tests for more images
* CI-unixish-docker.yml: adjusted some step checks
Oliver Stöneberg
Paul Fultz II
Daniel Marjamäki
Armin Müller