Pin kubernetes to a max version of 11.0.0. (apache#11974)

12.0.0 introduces `TypeError: cannot serialize '_io.TextIOWrapper'
object` when serializing V1Pod's in `executor_config`.

(cherry picked from commit 9687b3b)
(cherry picked from commit 509a097)

setup.py

@@ -343,7 +343,7 @@ def write_version(filename=os.path.join(*[my_dir, "airflow", "git_version"])):
 ]
 kubernetes = [
     'cryptography>=2.0.0',
-    'kubernetes>=3.0.0',
+    'kubernetes>=3.0.0, <12.0.0',
     'packaging>=19.1',
 ]
 ldap = [