Update python versions in tests.yml

[marcharper]

Adds 3.15 and removes 3.11, 3.12.

[marcharper]

There's some issue with the torch version:

py315: install_deps> python -I -m pip install black hypothesis isort mypy 'numpy>=2.1' pytest-cov pytest-randomly pytest-sugar 'torch>=2.6.0' types-setuptools
ERROR: Ignored the following versions that require a different python version: 1.21.2 Requires-Python >=3.7,<3.11; 1.21.3 Requires-Python >=3.7,<3.11; 1.21.4 Requires-Python >=3.7,<3.11; 1.21.5 Requires-Python >=3.7,<3.11; 1.21.6 Requires-Python >=3.7,<3.11; 1.26.0 Requires-Python >=3.9,<3.13; 1.26.1 Requires-Python >=3.9,<3.13
ERROR: Could not find a version that satisfies the requirement torch>=2.6.0 (from versions: none)
ERROR: No matching distribution found for torch>=2.6.0

[drvinceknight]

Apparently (from Claude) the next PyTorch release should fix this.