LAL SWIG bindings seg fault with numpy 1.20.0

The LAL SWIG bindings cause a segmentation fault at runtime when using numpy 1.20.0. This is demonstrated in our own CI pipeline: https://git.ligo.org/lscsoft/lalsuite/-/jobs/1173013.

I'm patching the conda builds to pin to numpy <1.20.0a0 at runtime.