Merge branch 'feature/add_qt6_to_arch' into 'master'

Add Qt6 to Arch images

See merge request docker-images/gr-build-images!21

arch-self-contained/Dockerfile

@@ -18,5 +18,6 @@ RUN pacman -Syu --noconfirm && \
         patch \
         pkgconf \
         qt5-base \
+        qt6-base \
         xorg-xrandr && \
     yes | pacman -Scc

arch-system-dependencies/Dockerfile

@@ -17,5 +17,6 @@ RUN pacman -Syu --noconfirm && \
         make \
         mesa \
         patch \
-        qt5-base && \
+        qt5-base \
+        qt6-base && \
     yes | pacman -Scc