Update CI to newer Qt6 (#139)

Author: grulja

.github/workflows/build.yaml

@@ -23,7 +23,7 @@ jobs:
         sudo apt install cmake make pkg-config libx11-dev xcb libx11-xcb-dev libxkbcommon-dev libgtk-3-dev sassc
 
     - name: Install Qt
-      uses: jurplel/install-qt-action@v2
+      uses: jurplel/install-qt-action@v3
       with:
         version: 5.15.2
 
@@ -57,7 +57,7 @@ jobs:
     - name: Install Qt
       uses: jurplel/install-qt-action@v3
       with:
-        version: 6.2.3
+        version: 6.5.0
 
     - name: Install Adwaita-qt
       run: |