handle unexpected error types opaquely

src/main.ts

@@ -60,8 +60,12 @@ async function run(): Promise<void> {
       core.setFailed(
         `Dependency review is not supported on this repository. Please ensure that Dependency graph is enabled, see https://github.com/${github.context.repo.owner}/${github.context.repo.repo}/settings/security_analysis`
       )
-    } else (error instanceof Error) {
+    } else {
-      core.setFailed(error.message)
+      if (error instanceof Error) {
+        core.setFailed(error.message)
+      } else {
+        core.setFailed('Unexpected fatal error')
+      }
     }
   }
 }