flake8: add exceptions for overly pedantic camelcase rules from pep8-naming (#11477)

Rules N813 and N814 prevented import statements like this:

  xml.etree.ElementTree as et
  xml.etree.ElementTree as ET

But both of those seem pretty reasonable.  We see no reason to require any camelcase import to be imported "as" a camelcase word.

.flake8_packages

@@ -20,5 +20,5 @@
 # - F821: undefined name `name`
 #
 [flake8]
-ignore = E129,E221,E241,E272,E731,W503,W504,F405,F821,F999
+ignore = E129,E221,E241,E272,E731,W503,W504,F405,F821,F999,N801,N813,N814
 max-line-length = 79