workflow: fix PR name and Action warnings

Author: Sk7Str1p3

.github/workflows/flake.yml

@@ -21,8 +21,7 @@ jobs:
         id: flake-upd
         uses: DeterminateSystems/update-flake-lock@v25
         with:
-          pr-title: "Update flake.lock to nixpkgs ${{ steps.flake-upd.outputs.commit-hash }}"
+          pr-title: "Update flake.lock to nixpkgs ${{ steps.flake-upd.outputs.pull-request-number }}"
           pr-labels: |
             dependencies
-          pr-rebase: true
-
+            nix