bugfix of gpu msd-afqmc; fix tutorial

[jiangtong1000]

1. fix msd-afqmc green's function with gpu
   change walker_batch.Ga.fill(0.0 + 0.0j) to walker_batch.Ga = xp.zeros_like(walker_batch.Ga)
   since cupy does not have cupy.ndarray.fill

2. fix initial walker of msd trial
   from

elif isinstance(trial, ParticleHole):
    initial_walker = numpy.hstack([trial.psi0a, trial.psi0b])

to

elif isinstance(trial, ParticleHole):
    initial_walker = numpy.hstack([trial.psi0a, trial.psi0b])
    random_walker = numpy.random.random(initial_walker.shape)
    initial_walker = initial_walker + random_walker
    initial_walker, _ = numpy.linalg.qr(initial_walker)

Otherwise cause issues.

3. fix the integration. In Update actions checkout and setup-python (fixes warning). #277, the msd example was disabled. Now fixed with the second point mentioned above.

4. Modify the example for running msd-afqmc with MPI / GPU

[jiangtong1000]

fix #326

[jiangtong1000]

I have to revert the initial walker setup for UHFWalkersParticleHole, otherwise it won't pass the comparison with legacy code (which is a bit dirty to change that). Currently, I added the init walker perturbation in the example file. This will be temporary fix.

[linusjoonho]

LGTM