ci: Add deps updator (#22)

Author: SnO2WMaN

.github/workflows/update-deps.yml

@@ -0,0 +1,44 @@
+name: Update Dependencies
+
+on:
+  workflow_dispatch:
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  update-deps:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Setup elan
+        run: |
+          curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh -s -- -y
+          echo "$HOME/.elan/bin" >> "$GITHUB_PATH"
+      - name: Run lake update
+        run: lake update
+      - name: Check for changes
+        id: check_changes
+        run: |
+          if git diff --quiet; then
+            echo "has_changes=false" >> $GITHUB_OUTPUT
+          else
+            echo "has_changes=true" >> $GITHUB_OUTPUT
+          fi
+
+      - name: Commit and create PR
+        if: steps.check_changes.outputs.has_changes == 'true'
+        uses: peter-evans/create-pull-request@v8
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          commit-message: "chore: Update dependencies at $(date +%Y/%m/%d)"
+          title: "chore: Update dependencies at $(date +%Y/%m/%d)"
+          branch: "update-deps-$(date +%s)"
+          delete-branch: true
+          body: |
+            Automated dependency updates via `lake update`.
+
+            Please review the changes to `lake-manifest.json`.