Update requirements_optional.txt

Author: LiamConnors

test_requirements/requirements_optional.txt

@@ -10,7 +10,7 @@ ipython
 jupyter
 anywidget
 scipy
-Shapely
+Shapely<2.1
 geopandas
 fiona<=1.9.6;python_version<="3.8"  # fiona>1.9.6 is not compatible with geopandas<1; geopandas>=1 is not compatible with python 3.8
 pyshp