Fix final Python 3.13 failure in pytorch environment

Remove mpi4py<4.0 upper bound from etc/environment-pytorch.yml that was
missed in the previous fix. This file was preventing Python 3.13 tests
from passing for the pytorch environment.

All environment files now match master's pattern: no upper bounds on
mpi4py or mpi4py-fft to allow compatibility with new Python versions.

Co-authored-by: pancetta <7158893+pancetta@users.noreply.github.com>

Author: Copilot

etc/environment-pytorch.yml

@@ -11,7 +11,7 @@ dependencies:
   - matplotlib>=3.0,<4.0
   - dill>=0.2.6
   - mpich
-  - mpi4py>=3.0.0,<4.0
+  - mpi4py>=3.0.0
   - pip
   - pip:
     - qmat>=0.1.8