MAINT Permission for GH token in stale.yml

See huggingface/peft#2061 for the equivalent PR
in PEFT.

This restores the functionality of the stale bot after permissions for
the token have been limited. The action still shows errors for PEFT but
the bot appears to work fine.

.github/workflows/stale.yml

@@ -9,6 +9,8 @@ jobs:
     name: Close Stale Issues
     if: github.repository == 'huggingface/diffusers'
     runs-on: ubuntu-latest
+    permissions:
+      issues: write
     env:
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     steps: