README: Update supported Python versions (googleapis#1100)

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Fixes #<issue_number_goes_here> 🦕

To match the Trove classifiers on PyPI:

![image](https://user-images.githubusercontent.com/1324225/148646991-cc536f1f-4389-4cd9-9995-276c9aa7245a.png)

https://pypi.org/project/google-cloud-bigquery/

Author: hugovk

README.rst

@@ -52,7 +52,7 @@ dependencies.
 
 Supported Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^
-Python >= 3.6, < 3.10
+Python >= 3.6, < 3.11
 
 Unsupported Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^