Updates gymnasium to v1.2.0 (#2852)

# Description

Updates gymnasium to 1.2.0, which includes a fix for memory leak when
recording videos during training with `--video`.

Fixes #1996 

## Type of change

<!-- As you go through the list, delete the ones that are not
applicable. -->

- 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 not work as expected)
- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

<!--
As you go through the checklist above, you can mark something as done by
putting an x character in it

For example,
- [x] I have done this task
- [ ] I have not done this task
-->

source/isaaclab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.40.11"
+version = "0.40.12"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/isaaclab/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.40.12 (2025-07-03)
+~~~~~~~~~~~~~~~~~~~~
+
+Changed
+^^^^^^^
+
+* Updated gymnasium to v1.2.0. This update includes fixes for a memory leak that appears when recording
+  videos with the ``--video`` flag.
+
+
 0.40.11 (2025-06-27)
 ~~~~~~~~~~~~~~~~~~~~
 

source/isaaclab/setup.py

@@ -27,7 +27,7 @@ INSTALL_REQUIRES = [
     # devices
     "hidapi==0.14.0.post2",
     # reinforcement learning
-    "gymnasium>=1.0",
+    "gymnasium==1.2.0",
     # procedural-generation
     "trimesh",
     "pyglet<2",