workflows: bump artifact actions

No breaking changes.

Signed-off-by: Benjamin Gilbert <bgilbert@cs.cmu.edu>

Author: bgilbert

.github/workflows/dco-check.yml

@@ -48,7 +48,7 @@ jobs:
         dco-check -v $args
         touch result/success
     - name: Upload result
-      uses: actions/upload-artifact@v4
+      uses: actions/upload-artifact@v5
       if: always()
       with:
         name: result

.github/workflows/dco-report.yml

@@ -34,7 +34,7 @@ jobs:
     if: ${{ github.event.workflow_run.event == 'pull_request' }}
     steps:
       - name: Download state
-        uses: actions/download-artifact@v5
+        uses: actions/download-artifact@v6
         with:
           name: result
           path: result