meta: tweak update-flake-lock action

.github/workflows/update-flake-lock.yaml

@@ -1,8 +1,8 @@
-name: update-flake-lock
+name: Update flake.lock
 on:
   workflow_dispatch: # allows manual triggering
   schedule:
-    - cron: '0 0 * * 0' # runs weekly on Sunday at 00:00
+    - cron: '0 0 * * 0'
 
 jobs:
   lockfile:
@@ -12,7 +12,11 @@ jobs:
         uses: actions/checkout@v2
       - name: Install Nix
         uses: cachix/install-nix-action@v16
+      - name: Get current date
+        id: date
+        run: echo "::set-output name=date::$(date +'%Y%m%d')"
       - name: Update flake.lock
         uses: DeterminateSystems/update-flake-lock@v13
         with:
-          pr-title: "Update flake.lock" # Title of PR to be created
+          pr-title: "Updates ${{ steps.date.outputs.date }}"
+          branch: "updates-${{ steps.date.outputs.date }}"