Add a raise for generate_projects if Python is too old (#29432)

* Add a raise for generate_projects if Python is too old

* Update the comment

* Resolve the YAPF difference between local 0.30 and kokoro's 0.30

* YAPF

tools/buildgen/generate_projects.py

@@ -25,6 +25,10 @@ from typing import Dict, List, Union
 import _utils
 import yaml
 
+if sys.version_info < (3, 6):
+    raise RuntimeError('Expected Python version > 3.6, but got %s at %s' %
+                       (sys.version_info, sys.executable))
+
 PROJECT_ROOT = os.path.join(os.path.dirname(os.path.abspath(__file__)), "..",
                             "..")
 os.chdir(PROJECT_ROOT)