Similar to aws/aws-sam-cli#8545, tools like uv will try and run the aws cli using the latest Python version matching `requires-python`, but `aws` doesn't work with 3.14 yet:
```console
❯ uvx --from git+https://github.com/aws/aws-cli@v2 aws
  × Failed to build `ruamel-yaml-clib==0.2.12`
  ├─▶ The build backend returned an error
  ╰─▶ Call to `setuptools.build_meta.build_wheel` failed (exit status: 1)

      [stderr]
      Traceback (most recent call last):
        File "<string>", line 14, in <module>
          requires = get_requires_for_build({})
        File "/Users/zsol/.cache/uv/builds-v0/.tmpMfFdkc/lib/python3.14/site-packages/setuptools/build_meta.py", line 331, in get_requires_for_build_wheel
          return self._get_build_requires(config_settings, requirements=[])
                 ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/Users/zsol/.cache/uv/builds-v0/.tmpMfFdkc/lib/python3.14/site-packages/setuptools/build_meta.py", line 301, in _get_build_requires
          self.run_setup()
          ~~~~~~~~~~~~~~^^
        File "/Users/zsol/.cache/uv/builds-v0/.tmpMfFdkc/lib/python3.14/site-packages/setuptools/build_meta.py", line 317, in run_setup
          exec(code, locals())
          ~~~~^^^^^^^^^^^^^^^^
        File "<string>", line 79, in <module>
      ImportError: cannot import name 'Str' from 'ast' (/Users/zsol/.local/share/uv/python/cpython-3.14.0-macos-aarch64-none/lib/python3.14/ast.py)

      hint: This usually indicates a problem with the package or the build environment.
  help: `ruamel-yaml-clib` (v0.2.12) was included because `awscli` (v2.33.1) depends on `ruamel-yaml-clib`
```

This is tracked in aws#9914, but until that's done, it's better to declare the supported Python versions correctly. This PR does that