Fix wheel test job

Author: simonbowly

.github/workflows/wheel-tests.yml

@@ -50,6 +50,7 @@ jobs:
       - name: Fetch dependencies for offline install
         run: |
           pip wheel --wheel-dir=dist matplotlib networkx plotly scikit-learn
+          pip wheel --wheel-dir=dist "plotly<6"
       - name: Install example dependencies
         run: |
           python -m pip install --find-links dist --no-index --only-binary=:all: gurobi-optimods[examples]