Only build upon push to main branch, not PR

Just had to have it there to test that it would work before pushing to
main :)

Author: c-salomonsen

.github/workflows/build-image.yml

@@ -4,8 +4,6 @@ name: Create and publish a Docker image
 on:
   push:
     branches: ['main']
-  pull_request:
-    branches: ['main']
 
 # Defines two custom environment variables for the workflow. These are used for the Container registry domain, and a name for the Docker image that this workflow builds.
 env: