build: only build on main brnach with tags

Author: Neunerlei

.github/workflows/publish-dockerimage.yml

@@ -4,7 +4,7 @@ on:
   workflow_dispatch:
   push:
     tags:
-      - '*'
+      - '[0-9]+.[0-9]+.[0-9]+'
     branches:
       - main
 
@@ -17,14 +17,15 @@ jobs:
       contents: read
       attestations: write
       id-token: write
+    if: ${{ github.ref == 'refs/heads/main' }}
     steps:
       - name: Check out the repo
         uses: actions/checkout@v4
 
       - name: Extract tag name
         id: tag
         shell: bash
-        run: echo "tag=${GITHUB_REF#refs/tags/}" >> $GITHUB_OUTPUT
+        run: echo "tag=${GITHUB_REF/refs\/tags\//}" >> $GITHUB_OUTPUT
 
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v2