CI: switch openSUSE build to Qt6

.github/workflows/nightly-opensuse-qt6.yml

-name: nightly-opensuse-qt6
-
-on:
-  schedule:
-    - cron: "32 2 * * *"
-  workflow_dispatch:
-
-env:
-  BUILDDIR: /build
-  SRCDIR: ${{ github.workspace }}
-  CMAKE_ARGS: |
-    -DKDE_INSTALL_USE_QT_SYS_PATHS=ON
-    -DCMAKE_BUILD_TYPE=Debug
-    -DWITH_QT6=ON
-
-jobs:
-  build:
-    runs-on: ubuntu-latest
-    container:
-      image: docker://opensuse/tumbleweed
-      options: --tmpfs /build:rw --user 0:0
-    steps:
-      - name: "prepare git"
-        shell: bash
-        run: zypper --non-interactive in git-core jq curl
-      - name: "prepare source"
-        uses: calamares/actions/generic-checkout@v5
-      - name: "install dependencies"
-        shell: bash
-        run: ./ci/deps-opensuse-qt6.sh
-      - name: "build"
-        shell: bash
-        run: ./ci/build.sh

.github/workflows/nightly-opensuse.yml

@@ -15,6 +15,7 @@ env:
     -DBUILD_TESTING=ON
     -DBUILD_APPSTREAM=ON
     -DBUILD_APPDATA=ON
+    -DWITH_QT6=ON
 
 jobs:
   build: