Fix workflow condition (#14)

Co-authored-by: Henrique Santos <henrique.santos@freiheit.com>

.github/workflows/release.yaml

@@ -7,8 +7,6 @@ on:
   push:
     tags:
       - 'v*'
-    branches:
-      - main
 
 # Releases need permissions to read and write the repository contents.
 # GitHub considers creating releases and uploading assets as writing contents.
@@ -19,6 +17,9 @@ jobs:
   goreleaser:
     runs-on: ubuntu-latest
     steps:
+      - name: Check if tag belongs to main branch
+        if: endsWith(github.ref, 'main') == false
+        run: exit -1
       - uses: actions/checkout@v3
         with:
           # Allow goreleaser to access older tag information.