Merge pull request #457 from crazy-max/fix-github-ref-pr

context: fix pull request ref

src/context.ts

@@ -45,6 +45,8 @@ export class Context {
     }
     if (github.context.sha && !gitRef.startsWith(`refs/pull/`)) {
       gitRef = github.context.sha;
+    } else if (gitRef.startsWith(`refs/pull/`)) {
+      gitRef = gitRef.replace(/\/merge$/g, '/head');
     }
     return gitRef;
   }