Minor fix for documentation link (#15221)

CONTRIBUTING.md

@@ -14,7 +14,7 @@ are important to the project's success.
       but [contact us](README.md#discussion) before starting significant work.
     * Create your stubs, considering [what to include](#what-to-include) and
       conforming to the [coding style](https://typing.readthedocs.io/en/latest/guides/writing_stubs.html#style-guide).
-4. Optionally [format and check your stubs](#code-formatting).
+4. Optionally [format and check your stubs](#stub-content-and-style).
 5. Optionally [run the tests](tests/README.md).
 6. [Submit your changes](#submitting-changes) by opening a pull request.
 7. Make sure that all tests in CI are passing.