Properly create workspace in OS tmpdir for generate-patch command

Signed-off-by: Fredrik Adelöw <freben@gmail.com>

.changeset/neat-pens-clean.md

@@ -0,0 +1,5 @@
+---
+'@backstage/repo-tools': patch
+---
+
+Properly create workspace in OS temporary directory for `generate-patch` command

packages/repo-tools/src/commands/generate-patch/generate-patch.ts

@@ -98,7 +98,9 @@ export default async (
     throw new Error(`Could not find package ${packageArg} in source repo`);
   }
 
-  const tmpDir = await fs.mkdtemp(os.tmpdir());
+  const tmpDir = await fs.mkdtemp(
+    joinPath(os.tmpdir(), 'backstage-repo-tools-generate-patch-'),
+  );
   const ctx: PatchContext = {
     sourceRepo,
     targetRepo,