Bump minimum torch version from 2.3 to 2.8 to address GHSA-887c-mr87-cxwp

[JacopoPan]

Description

Dependabot raised transitive dependency alerts in repos depending on SB3 because of GHSA-887c-mr87-cxwp

Motivation and Context

Closes #2250

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist

• I've read the CONTRIBUTION guide (required)
• I have updated the changelog accordingly (docs/misc/changelog.md) (required).
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have opened an associated PR on the SB3-Contrib repository (if necessary)
• I have opened an associated PR on the RL-Zoo3 repository (if necessary)
• I have reformatted the code using make format (required)
• I have checked the codestyle using make check-codestyle and make lint (required)
• I have ensured make pytest and make type both pass. (required)
• I have checked that the documentation builds using make doc (required)

[JacopoPan]

@araffin

as mentioned in #2250 I have simply bumped pytorch from 2.3 to 2.8 to address GHSA-887c-mr87-cxwp

However, I noted that in

stable-baselines3/docs/conda_env.yml

Lines 2 to 9 in 40da841

	channels:
	- pytorch
	- conda-forge
	dependencies:
	- cpuonly=1.0=0
	- pip=24.2
	- python=3.11
	- pytorch=2.5.0=py3.11_cpu_0

channel pytorch is used (with the specific naming for its packages in line 9) but it only contains packages up to version 2.5.1, while newer versions are in channels main and conda-forge

• https://anaconda.org/channels/pytorch/packages/pytorch/overview
• https://anaconda.org/channels/main/packages/pytorch/overview
• https://anaconda.org/channels/conda-forge/packages/pytorch/overview

I removed channel pytorch to use version 2.9.1 from conda-forge as in the CI

stable-baselines3/.github/workflows/ci.yml

Line 44 in 40da841

uv pip install --system torch==2.9.1+cpu --index https://download.pytorch.org/whl/cpu

but I don't know if maybe you want to handle it differently