ci: add stale PR workflow (foundry-rs#14832)

* ci: add stale PR workflow

* Update .github/workflows/stale-prs.yml

Co-authored-by: zerosnacks <95942363+zerosnacks@users.noreply.github.com>

* ci: remove stale label creation

* ci: use stale action for PRs

* Apply suggestion from @zerosnacks

* Apply suggestion from @zerosnacks

---------

Co-authored-by: zerosnacks <95942363+zerosnacks@users.noreply.github.com>

Author: emmajam

.github/workflows/stale-prs.yml

@@ -0,0 +1,32 @@
+# Marks pull requests as stale.
+
+name: stale PRs
+
+on:
+  workflow_dispatch: {}
+  schedule:
+    - cron: "30 1 * * *"
+
+permissions: {}
+
+jobs:
+  stale-prs:
+    if: github.repository == 'foundry-rs/foundry'
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      pull-requests: write
+    steps:
+      - uses: actions/stale@b5d41d4e1d5dceea10e7104786b73624c18a190f # v10.2.0
+        with:
+          days-before-issue-stale: -1
+          days-before-issue-close: -1
+          days-before-pr-stale: 14
+          days-before-pr-close: 7
+          stale-pr-label: "stale"
+          exempt-pr-labels: "stop-stale"
+          stale-pr-message: "This pull request is stale because it has been open for 14 days with no activity. It will be closed in 7 days if there is no further activity."
+          close-pr-message: "This pull request was closed because it has been inactive for 7 days since being marked as stale."
+          labels-to-add-when-unstale: "stop-stale"
+          exempt-all-milestones: true
+          exempt-all-assignees: true