scaffolder-backend: fix error behaviour in runCommand helper

Signed-off-by: David Dyball <david.dyball@gmail.com>

.changeset/brown-impalas-greet.md

@@ -0,0 +1,6 @@
+---
+'@backstage/plugin-scaffolder-backend': patch
+---
+
+Fix error handling of the `runCommand` helper to return `Error`
+instance.

plugins/scaffolder-backend/src/scaffolder/actions/builtin/helpers.ts

@@ -58,7 +58,9 @@ export const runCommand = async ({
 
     process.on('close', code => {
       if (code !== 0) {
-        return reject(`Command ${command} failed, exit code: ${code}`);
+        return reject(
+          new Error(`Command ${command} failed, exit code: ${code}`),
+        );
       }
       return resolve();
     });