Change push to only main branch for Build GHCR workflow (#58)

Author: vgrassia

.github/workflows/build-ghcr.yml

@@ -1,7 +1,10 @@
+---
 name: Build for GitHub Container Registry
 
 on:
   push:
+    branches:
+      - "main"
   workflow_dispatch:
 
 jobs:

.github/workflows/build.yml

@@ -1,3 +1,4 @@
+---
 name: Build
 
 on:

.github/workflows/bump-version.yml

@@ -1,3 +1,4 @@
+---
 name: Bump version
 
 on:

.github/workflows/release.yml

@@ -1,3 +1,4 @@
+---
 name: Release
 run-name: Release ${{ github.event.inputs.release_type }}