Bump typed-ast version, recommend Python 3.8 for tests (#6278)

CONTRIBUTING.md

@@ -27,8 +27,9 @@ it takes a bit longer. For more details, read below.
 To reformat the code, check for common problems, and
 run the tests, you need to prepare a
 [virtual environment](https://docs.python.org/3/tutorial/venv.html)
-with the necessary libraries installed. To do this, run:
+with the necessary libraries installed using Python 3.8 or newer.
 
+To do this, run:
 ```
 $ python3 -m venv .venv3
 $ source .venv3/bin/activate

requirements-tests-py3.txt

@@ -1,6 +1,5 @@
 mypy==0.910
 pytype==2021.11.2
-typed-ast==1.4.3
 black==21.9b0
 flake8==4.0.1
 flake8-bugbear==21.9.2

stubs/typed-ast/METADATA.toml

@@ -1 +1 @@
-version = "1.4.*"
+version = "1.5.*"

tests/README.md

@@ -13,7 +13,7 @@ objects at runtime.
 objects at runtime.
 
 To run the tests, follow the [setup instructions](../CONTRIBUTING.md#preparing-the-environment)
-in the `CONTRIBUTING.md` document.
+in the `CONTRIBUTING.md` document. In particular, we recommend running with Python 3.8 or newer.
 
 ## mypy\_test.py