Update 'typing_extensions' to >=4.6.0 to fix python 3.12 error (#17312)

With earlier versions of typing_extensions, the following traceback is
seen:

```
Traceback (most recent call last):
  File ".../bin/mypy", line 5, in <module>
    from mypy.__main__ import console_entry
  File ".../lib/python3.12/site-packages/mypy/__main__.py", line 9, in <module>
    from mypy.main import main, process_options
  File ".../lib/python3.12/site-packages/mypy/main.py", line 12, in <module>
    from typing_extensions import Final
  File ".../lib/python3.12/site-packages/typing_extensions.py", line 1174, in <module>
    class TypeVar(typing.TypeVar, _DefaultMixin, _root=True):
TypeError: type 'typing.TypeVar' is not an acceptable base type
```

The error is addressed in typing_extensions in
 python/typing_extensions#162, which is included
in the 4.6.0 release.

mypy-requirements.txt

@@ -1,4 +1,4 @@
 # NOTE: this needs to be kept in sync with the "requires" list in pyproject.toml
-typing_extensions>=4.1.0
+typing_extensions>=4.6.0
 mypy_extensions>=1.0.0
 tomli>=1.1.0; python_version<'3.11'

pyproject.toml

@@ -6,7 +6,7 @@ requires = [
     "setuptools >= 40.6.2",
     "wheel >= 0.30.0",
     # the following is from mypy-requirements.txt
-    "typing_extensions>=4.1.0",
+    "typing_extensions>=4.6.0",
     "mypy_extensions>=1.0.0",
     "tomli>=1.1.0; python_version<'3.11'",
     # the following is from build-requirements.txt