ci: fix GitHub Actions runner configuration

Replaces invalid 'ubuntu-slim' runner with 'ubuntu-latest' to ensure the duplicate issues workflow executes properly.

The ubuntu-slim runner type does not exist in GitHub Actions, causing workflow failures.

Author: miantiao-me

.github/workflows/duplicate-issues.yml

@@ -6,7 +6,7 @@ on:
 
 jobs:
   check-duplicates:
-    runs-on: ubuntu-slim
+    runs-on: ubuntu-latest
     permissions:
       contents: read
       issues: write