FIX: Adding build_ext call to setup.py on release

We need to call build_ext before creating the sdist so that
we can have the Cython built extensions available. This eliminates
the need to have Cython to install Cartopy.

.github/workflows/release.yml

@@ -31,7 +31,7 @@ jobs:
           conda install $PACKAGES
 
       - name: Create sdist
-        run: python setup.py sdist
+        run: python setup.py build_ext sdist
 
       - name: Publish Package
         uses: pypa/gh-action-pypi-publish@master