Fix sending slack message on failure (#3964)

#### Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No

#### Type of change

- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [x] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Test Plan

- [x] 💪 Manual
- [ ] ⚡ Unit test
- [ ] 💚 E2E

.github/workflows/longevity_test.yml

@@ -61,7 +61,13 @@ jobs:
         run: |
           echo version=$(git describe --tags --abbrev=0) | tee -a $GITHUB_OUTPUT
 
-      - run: git checkout ${{ steps.version.outputs.version }}
+      # Checkout the .github directory at the original branch's ref so we have a
+      # stable view of the actions.
+      - name: Code Checkout
+        working-directory: ${{ github.workspace }}
+        run: |
+          git checkout ${{ steps.version.outputs.version }}
+          git checkout ${{ github.ref }} -- .github
 
       - run: go build -o corso