Tweak release body text, add way to dry run action workflow

.github/workflows/build_app.yml

@@ -10,6 +10,9 @@ on:
       git-ref:
         description: Git Ref (Optional)
         required: false
+      dry-run:
+        description: Creates a draft release
+        required: false
 
 jobs:
   build-app:
@@ -53,8 +56,11 @@ jobs:
         with:
           tag_name: r${{ env.COMMIT_COUNT }}
           release_name: Tachiyomi Preview r${{ env.COMMIT_COUNT }}
-          body: 'r${{ env.COMMIT_COUNT }}\n\nLatest commit: https://github.com/inorichi/tachiyomi/commit/${{ env.CURRENT_SHA }}'
-          draft: false
+          body: >
+            r${{ env.COMMIT_COUNT }}
+
+            Latest commit: https://github.com/inorichi/tachiyomi/commit/${{ env.CURRENT_SHA }}
+          draft: ${{ github.event.inputs.dry-run != '' }}
           prerelease: false
       - name: Upload APK to release
         uses: actions/upload-release-asset@v1