Officially remove Python 3.9 support

Part of #13782

Author: srittau

CONTRIBUTING.md

@@ -55,8 +55,6 @@ Note that some tests require extra setup steps to install the required dependenc
   <td>Linux / macOS / WSL</td>
   <td>
 
-  On Linux and macOS, you will be able to run the full test suite on Python
-  3.9-3.12.
   To install the necessary requirements, run the following commands from a
   terminal window:
 

README.md

@@ -21,7 +21,7 @@ the project the stubs are for, but instead report them here to typeshed.**
 Further documentation on stub files, typeshed, and Python's typing system in
 general, can also be found at https://typing.readthedocs.io/en/latest/.
 
-Typeshed supports Python versions 3.9 to 3.14.
+Typeshed supports Python versions 3.10 to 3.14.
 
 ## Using
 

pyproject.toml

@@ -263,4 +263,4 @@ extra-standard-library = [
 known-first-party = ["_utils", "ts_utils"]
 
 [tool.typeshed]
-oldest_supported_python = "3.9"
+oldest_supported_python = "3.10"