Backport PR matplotlib#28023: ci: Update merge conflict labeler

Author: dstansby

.github/workflows/conflictcheck.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check if PRs have merge conflicts
-        uses: eps1lon/actions-label-merge-conflict@releases/2.x
+        uses: eps1lon/actions-label-merge-conflict@e62d7a53ff8be8b97684bffb6cfbbf3fc1115e2e  # v3.0.0
         with:
           dirtyLabel: "status: needs rebase"
           repoToken: "${{ secrets.GITHUB_TOKEN }}"