Decrease version to 6.6

Reason: Because with 6.8 there are fetch errors with Qt install
INFO    : aqtinstall(aqt) v3.1.21 on Python 3.9.16 [CPython GCC 11.3.1 20221121 (Red Hat 11.3.1-4)]
INFO    : Downloading qtwebengine...
INFO    : Downloading qtdeclarative...
INFO    : Downloading qtbase...
INFO    : Downloading qtsvg...
INFO    : Redirected: qt-mirror.dannhauer.de
INFO    : Redirected: qt-mirror.dannhauer.de
INFO    : Redirected: qt-mirror.dannhauer.de
INFO    : Redirected: qt-mirror.dannhauer.de
INFO    : Finished installation of qtsvg-Linux-RHEL_8_6-GCC-Linux-RHEL_8_6-X86_64.7z in 0.66724220
^CWARNING : Caught KeyboardInterrupt, terminating installer workers
ERROR   : Installer halted by keyboard interrupt.
muc93k068:/home/mmarmsol/Documents/Temp/Qt $ python -m aqt install-qt linux desktop 6.7.0 gcc_64 --autodesktop --outputdir .  --modules qtwebengine
INFO    : aqtinstall(aqt) v3.1.21 on Python 3.9.16 [CPython GCC 11.3.1 20221121 (Red Hat 11.3.1-4)]
ERROR   : The packages ['qt_base', 'qtwebengine'] were not found while parsing XML of package information!
==============================Suggested follow-up:==============================
* Please use 'aqt list-qt linux desktop --arch 6.7.0' to show architectures available.
* Please use 'aqt list-qt linux desktop --modules 6.7.0 <arch>' to show modules available.

.github/workflows/build.yml

@@ -120,7 +120,7 @@ jobs:
       fail-fast: false
       matrix:
         qt:
-          - version: 6.8.0
+          - version: 6.6.0
 
         env:
           - name: linux