Drop support for Python 3.7.

Python 3.7 reaches end-of-life on 27 June 2023 (https://devguide.python.org/versions/), and future versions of MuJoCo (after 2.3.6) will no longer support it.

PiperOrigin-RevId: 543594006
Change-Id: I66a7db3dab5d08f2fc52912c43e1532080600fc8

python/setup.py

@@ -363,7 +363,6 @@ SETUP_KWARGS = dict(
         'License :: OSI Approved :: Apache Software License',
         'Natural Language :: English',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3.10',
@@ -385,7 +384,7 @@ SETUP_KWARGS = dict(
         CMakeExtension('mujoco._simulate'),
         CMakeExtension('mujoco._structs'),
     ],
-    python_requires='>=3.7',
+    python_requires='>=3.8',
     install_requires=[
         'absl-py',
         'glfw',