Revert "Bump MuJoCo version to 3.2.6."

[MichaelMarav]

Current latest mujoco release is 3.2.5. This PR reverts the commit that bumps the version to 3.2.6 causing issues when trying to install the unity plugin.

Reverted commit: 276f5b0.

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[Balint-H]

Hello! MuJoCo as a library is continually developed, and so is the Unity plugin. During this process the version of the engine will necessarily increase, and the Unity plugin may not be always up to date and compatible with the newest version on the main branch.

In general, do not download the Unity package from the main branch of the repository (which may be in a work-in-progress state), instead pick the last stable tag of the repository. You can clone the repo and checkout the previous releases' tag (e.g., git checkout 3.2.5), or directly reference the tag in your Unity project manifest (in which case you don't need to manually clone the repo, add the line "org.mujoco": "https://github.com/google-deepmind/mujoco.git?path=unity#3.2.5", to your manifest file in the Unity project's "Packages" folder). Always remember to add the correct .dll file to your package as well.

If you are looking for a stable development experience, I recommend sticking to a release or two behind the newest one when using the Unity plugin, as it has less rigorous testing than the main engine. 3.2.5 I've tested to work well in my test scenes.

Of course, if you need a feature available in the newest version of MuJoCo and it is not available or buggy in the plugin, the that's a different issue. In that case please submit a bug report issue.

[Balint-H]

I'm closing this PR for now. If I have misunderstood your concern, let me know and we can reopen it.

[MichaelMarav]

The problem I am mentioning in this PR is not that Unity was not up-to-date with the latest MuJoCo release. The problem was the version Unity was referencing was ahead of the latest mujoco release (which at the time I opened the PR was 3.2.5). However, after the latest release of 3.2.6, the same issue arises with package.json referencing 3.2.7.
"name": "org.mujoco",
"displayName": "MuJoCo",
"version": "3.2.7",

[Balint-H]

That is intended, after the release of 3.2.6, main is now working on creating Release 3.2.7. Part of that work is updating the Plugin to 3.2.7.

You should be using a release version of the repo, not main. E.g., take a look at the 3.2.6 version of the package:

https://github.com/google-deepmind/mujoco/blob/3.2.6/unity/Runtime/Bindings/MjBindings.cs
https://github.com/google-deepmind/mujoco/blob/3.2.6/unity/package.json

They all refer to 3.2.6.

However, this is not made clear in the Unity-plugin documentation. I'll send a PR in the coming days to clarify that the main branch should not be used for the package, rather one of the release tags must be used to find the appropriate commit of the repo.