Restrict release workflow to pushes

The release workflow should not run on pull requests.

Author: jschwe

.github/workflows/release.yml

@@ -39,7 +39,6 @@ permissions:
 # If there's a prerelease-style suffix to the version, then the release(s)
 # will be marked as a prerelease.
 on:
-  pull_request:
   push:
     tags:
       - '**[0-9]+.[0-9]+.[0-9]+*'