Merge branch 'fix/arch-build-images' into 'master'

Add missing `which` in Arch images

See merge request docker-images/gr-build-images!29

arch-self-contained/Dockerfile

@@ -19,5 +19,6 @@ RUN pacman -Syu --noconfirm && \
         pkgconf \
         qt5-base \
         qt6-base \
+        which \
         xorg-xrandr && \
     yes | pacman -Scc

arch-system-dependencies/Dockerfile

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