fix ref for pr closed event when a pr is merged (#141)

src/input-helper.ts

@@ -61,6 +61,12 @@ export function getInputs(): ISourceSettings {
     if (isWorkflowRepository) {
       result.ref = github.context.ref
       result.commit = github.context.sha
+
+      // Some events have an unqualifed ref. For example when a PR is merged (pull_request closed event),
+      // the ref is unqualifed like "master" instead of "refs/heads/master".
+      if (result.commit && result.ref && !result.ref.startsWith('refs/')) {
+        result.ref = `refs/heads/${result.ref}`
+      }
     }
 
     if (!result.ref && !result.commit) {