ci: add weekly workflow to test against latest dependencies

Runs every Monday with `uv sync --upgrade` to catch upstream breakage
early, testing on Python 3.10 and 3.13.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: FBumann

.github/workflows/latest-deps.yml

@@ -0,0 +1,33 @@
+name: Test Latest Dependencies
+
+on:
+  schedule:
+    # Every Monday at 07:00 UTC
+    - cron: "0 7 * * 1"
+  workflow_dispatch:
+
+jobs:
+  test-latest:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.10", "3.13"]
+
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v7
+
+      - name: Set up Python ${{ matrix.python-version }}
+        run: uv python install ${{ matrix.python-version }}
+
+      - name: Install with latest dependencies
+        run: uv sync --extra dev --upgrade
+
+      - name: Test
+        run: uv run pytest --cov=xarray_plotly
+
+      - name: Print dependency versions
+        if: always()
+        run: uv pip list | grep -iE "xarray|plotly|pandas"