Unpin Shapely requirement in test_requirements/requirements_optional.txt

[marthacryan]

Shapely gives different outputs between versions 2.1 and <2.1, but python <=3.9 CI pipelines were failing because they're using a different version of Shapely from python>3.9 CI pipelines. We should figure out how to handle this without pinning requirements

[marthacryan]

I pinned the requirement in #5096.