fix(ci): do not auto stale issues (canonical#5775)

days-before-{stale,close} seems to activate auto staleing of issues.
Demote them to days-before-pr{stale,close} to only act upon PRs.

Rereferences:

- [1] https://github.com/actions/stale
- [2] https://github.com/actions/stale/blob/main/action.yml

.github/workflows/stale.yml

@@ -13,8 +13,10 @@ jobs:
     - uses: actions/stale@v9
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
-        days-before-stale: 14
-        days-before-close: 7
+        days-before-issue-stale: -1
+        days-before-issue-close: -1
+        days-before-pr-stale: 14
+        days-before-pr-close: 7
         stale-pr-message: |
           Hello! Thank you for this proposed change to cloud-init. This pull request is now marked as stale as it has not seen any activity in 14 days. If no activity occurs within the next 7 days, this pull request will automatically close.