Modifying the conditions in which ci workflow is run

.github/workflows/build.yml

@@ -1,17 +1,14 @@
 # This file was modified from ProofWidgets4's build.yml code
 on:
   push:
-    branches:
-      - duper
   pull_request:
-    branches:
-      - duper
 
 name: ci
 
 jobs:
   build:
     name: ${{ matrix.name }}
+    if: github.ref_type == 'tag'
     runs-on: ${{ matrix.os }}
     defaults:
       run: