Guard release job against non-dispatch triggers

GitHub creates a check run for modified workflow files on push
even when the file only triggers on workflow_dispatch. The run
fails because inputs.version is undefined in a push context.

Author: bschwedler

.github/workflows/release.yml

@@ -10,6 +10,7 @@ on:
 
 jobs:
   release:
+    if: github.event_name == 'workflow_dispatch'
     timeout-minutes: 10
     permissions:
       contents: write