ci(release): enable universe repo for .deb build (Plasma/KF6)

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: fuddlesworth

.github/workflows/release.yml

@@ -50,6 +50,12 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Enable universe (Plasma/KF6)
+        run: |
+          # Plasma 6 / KF6 packages are in the community-maintained universe repo
+          sed -i 's/^deb \(.*\) main$/deb \1 main universe/' /etc/apt/sources.list
+          apt-get update
+
       - name: Install build dependencies
         run: |
           apt-get install -y --no-install-recommends \