Fix release CI workflow

[janosh]

I'm a bit confused after #2726 (comment). As I understand the docs, pyproject.toml's [build-system].requires is supposed to already handle installing numpy and cython prior to running setup.py so there should be no need for fetch_build_eggs.

But the failed release workflow suggests that's not happening. I think the only reason this hasn't come up in CI before is that the test.yml workflow installs m3gnet first, then pymatgen and m3gnet comes with numpy. Before #2707, all CI workflows installed requirements.txt first before running pip install . so unless I'm mistaken, the build-system.require hasn't actually setup the build-time requirements for a while?

pymatgen/.github/workflows/test.yml

Lines 51 to 55 in d17a0f4

	run: |
	pip install --upgrade pip wheel
	pip install m3gnet
	pip install -e '.[dev,optional]'
	- name: pytest split ${{ matrix.split }}

[janosh]

@shyuep Maybe we use this hack in setup.py for now so we no longer rely on some other pip command installing numpy first before pip install .?

import subprocess

try:
    import numpy
except ImportError:
    subprocess.run(['pip', 'install', 'numpy'])
    import numpy

[coveralls]

Coverage remained the same at 0.0% when pulling 32068db on fix-release-wf into d17a0f4 on master.