ci: move source archive to run only for appimage build

The nightly builds seem to often trip over each other when
uploading the source tarball from ubuntu20.

Restrict it to being built only on the appimage build (ubuntu16).

ci/deploy.sh

@@ -134,8 +134,6 @@ EOF
         rm -rf pkg
       ;;
     esac
-    ./ci/source-archive.sh
-
     ;;
   *)
     ;;

ci/generate-workflows.py

@@ -251,6 +251,7 @@ cargo build --all --release""",
     def package(self):
         steps = [RunStep("Package", "bash ci/deploy.sh")]
         if self.app_image:
+            steps.append(RunStep("Source Tarball", "bash ci/source-archive.sh"))
             steps.append(RunStep("Build AppImage", "bash ci/appimage.sh"))
         return steps