fix(ci/github/agent-container): set the right build conditionals

Author: ayuskauskas

.github/workflows/agent-container.yaml

@@ -2,7 +2,14 @@ name: Build and push agent container image
 
 # Configures this workflow to run every time a tag is created
 on:
+  pull_request:
+    branches:
+      - main
   push:
+    branches:
+      - main
+    tags:
+      - agent/*
     paths:
       - agent/**
       - containers/agent.Dockerfile
@@ -20,7 +27,7 @@ env:
 # There is a single job in this workflow. It's configured to run on the latest available version of Ubuntu.
 jobs:
   build-and-push-agent:
-    if: ${{ ! startsWith(github.ref, 'refs/tags/operator') }}
+    if: ${{ (! startsWith(github.ref, 'refs/tags/operator')) && ( startsWith(github.ref, 'pull/') || github.ref == 'refs/heads/main')}}
     runs-on: ubuntu-latest
     # Sets the permissions granted to the `GITHUB_TOKEN` for the actions in this job.
     permissions: