Only trigger the pre-release generation when in 'main'

.github/workflows/ci.yml

@@ -215,6 +215,7 @@ jobs:
   prerelease-head:
     name: Create a GitHub prerelease with the binary artifacts
     runs-on: ubuntu-latest
+    if: github.ref == 'refs/heads/main'
     needs: ["build", "build-alpine"]
     permissions:
       contents: write