ci: bump upload-artifact to v6 for newer Node runtime

.github/workflows/appimage-build.yml

@@ -217,7 +217,7 @@ jobs:
           subject-path: Zoitechat-*-x86_64.AppImage
 
       - name: Upload AppImage artifact
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: zoitechat-appimage
           path: Zoitechat-*-x86_64.AppImage

.github/workflows/flatpak-build.yml

@@ -36,7 +36,7 @@ jobs:
 
       - name: Upload Flatpak Bundle
         id: upload_flatpak
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: zoitechat.flatpak
           path: zoitechat.flatpak

.github/workflows/manjaro-package-build.yml

@@ -74,7 +74,7 @@ jobs:
           cp -v "$GITHUB_WORKSPACE"/packaging/manjaro/.SRCINFO artifacts/
 
       - name: Upload package artifacts
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: zoitechat-manjaro-package
           path: artifacts/*

.github/workflows/windows-build.yml

@@ -143,7 +143,7 @@ jobs:
 
       - name: Upload Installer
         id: upload_installer
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: Installer ${{ matrix.arch }}
           path: ZoiteChat-*.exe
@@ -157,7 +157,7 @@ jobs:
 
       - name: Upload Build Files
         id: upload_buildfiles
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: Build Files ${{ matrix.arch }}
           path: zoitechat-build