Merge pull request #180 from DiamondLightSource/ci

Run the tests on the `main` branch only once

Author: namannimmo10

.github/workflows/httomolibgpu_tests_run_iris.yml

@@ -1,8 +1,5 @@
 name: httomolibgpu tests
 on:
-  push:
-    branches:
-      - main
   pull_request:
     branches:
       - main