Numpy 2.0.0 breaks our environment

[sapols]

Broke in run 189: https://github.com/heliophysicsPy/pyhc-docker-environment/actions/runs/9543369553

Idk what the exact problem/fix is yet.

[sapols]

Seems all that happened was numpy 2.0.0 was getting pulled in as a pipeline dependency, which broke the first pandas import statement in pipeline.py. Adding numpy<2.0.0 to the top of pipeline-requirements.txt fixed it.

However, because apparently no packages currently have a numpy<2 upper bound, version 2.0.0 is getting installed into the environment, which breaks things when you go to use it. We'll have to manually add that upper bound, for now.

[sapols]

Temporarily specifying that our environment use numpy==1.26.4 (the latest version before 2) by adding specify_numpy_1_26_4(docker_requirements_path) to pipeline.py.