Add Ubuntu 26.04 "Resolute Racoon" build (#6766)

* Create 26.04 Dockerfile

* Update desktop-build.yml

* Update release_template.md

* Add ca-certificates package to build

.github/workflows/desktop-build.yml

@@ -142,11 +142,16 @@ jobs:
           - distro: Ubuntu
             version: 22.04
             package: DEB
+            test: skip    # Running tests on all distros is superfluous
 
           - distro: Ubuntu
             version: 24.04
             package: DEB
 
+          - distro: Ubuntu
+            version: 26.04
+            package: DEB
+
     name: ${{matrix.distro}} ${{matrix.version}}
     needs: configure
     runs-on: ubuntu-latest