Fix oss test issues.

* Bump Python 3.7 version.
* typing.final -> typing_extensions.final.

Author: rchen152

pytype/pytype_source_utils.py

@@ -126,7 +126,7 @@ def list_pytype_files(suffix):
 
 # When our open-source tests run on GitHub Actions, we install a Python 3.7
 # interpreter for vm_test.
-CUSTOM_PY37_EXE = "/opt/hostedtoolcache/Python/3.7.12/x64/bin/python3.7"
+CUSTOM_PY37_EXE = "/opt/hostedtoolcache/Python/3.7.13/x64/bin/python3.7"
 
 
 def get_custom_python_exe(python_version):

pytype/tests/test_pickle1.py

@@ -189,7 +189,7 @@ def f(x: UserDict.UserDict) -> None: ...
 
   def test_class_decorator(self):
     foo = """
-      from typing import final
+      from typing_extensions import final
       @final
       class A:
         def f(self): ...