Convert Python type hinting to be PEP-585 Compliant (#4083)

Python [PEP-585](https://peps.python.org/pep-0585/) replaces a number of
`typing` module types with built-in equivalents and `collections.abc`
versions as of Python 3.9, with the aim of eventually removing the
`typing` module versions of these classes altogether. Since the minimum
required version of Python listed in the [Contribution Tools
document](https://github.com/carbon-language/carbon-lang/blob/trunk/docs/project/contribution_tools.md#main-tools)
is 3.9, the type hints in the various python files in the repo can be
updated to this style of type hint without a need for backwards
compatibility.

Feel free to close if this isn't a desired change at this time!

---------

Co-authored-by: Jon Ross-Perkins <jperkins@google.com>

github_tools/github_helpers.py

@@ -10,8 +10,9 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 """
 
 import argparse
+from collections.abc import Generator
 import os
-from typing import Dict, Generator, Optional, Tuple
+from typing import Optional
 
 # https://pypi.org/project/gql/
 import gql  # type: ignore
@@ -54,16 +55,16 @@ class Client:
         )
         self._client = gql.Client(transport=transport)
 
-    def execute(self, query: str) -> Dict:
+    def execute(self, query: str) -> dict:
         """Runs a query."""
         return self._client.execute(gql.gql(query))  # type: ignore
 
     def execute_and_paginate(
         self,
         query: str,
-        path: Tuple[str, ...],
-        first_page: Optional[Dict] = None,
-    ) -> Generator[Dict, None, None]:
+        path: tuple[str, ...],
+        first_page: Optional[dict] = None,
+    ) -> Generator[dict, None, None]:
         """Runs a query with pagination.
 
         Arguments: