Post release version update: Update to V3.1.2

PiperOrigin-RevId: 592019826
Change-Id: I64fd7da628bf3312ede4970b9b10ef5d0cc75b45

doc/APIreference/APIglobals.rst

@@ -522,7 +522,7 @@ shown in the table below. Their names are in the format ``mjKEY_XXX``. They corr
      - Maximum number of UI rectangles.
        Defined in `mjui.h <https://github.com/google-deepmind/mujoco/blob/main/include/mujoco/mjui.h>`_.
    * - ``mjVERSION_HEADER``
-     - 311
+     - 312
      - The version of the MuJoCo headers; changes with every release. This is an integer equal to 100x the software
        version, so 210 corresponds to version 2.1. Defined in  mujoco.h. The API function :ref:`mj_version` returns a
        number with the same meaning but for the compiled library.

doc/unity.rst

@@ -30,14 +30,14 @@ _____
 
 The MuJoCo app needs to be run at least once before the native library can be used, in order to register the library as
 a trusted binary. Then, copy the dynamic library file from
-``/Applications/MuJoCo.app/Contents/Frameworks/mujoco.framework/Versions/Current/libmujoco.3.1.1.dylib`` (it can be
+``/Applications/MuJoCo.app/Contents/Frameworks/mujoco.framework/Versions/Current/libmujoco.3.1.2.dylib`` (it can be
 found by browsing the contents of ``MuJoCo.app``) and rename it as ``mujoco.dylib``.
 
 Linux
 _____
 
 Expand the ``tar.gz`` archive to ``~/.mujoco``. Then copy the dynamic library from
-``~/.mujoco/mujoco-3.1.1/lib/libmujoco.so.3.1.1`` and rename it as ``libmujoco.so``.
+``~/.mujoco/mujoco-3.1.2/lib/libmujoco.so.3.1.2`` and rename it as ``libmujoco.so``.
 
 Windows
 _______