iotests/297: add --namespace-packages to mypy arguments

mypy is kind of weird about how it handles imports. For legacy reasons,
it won't load PEP 420 namespaces, because of logic implemented prior to
that becoming a standard.

So, if you plan on using any, you have to pass
--namespace-packages. Alright, fine.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Message-id: 20210527211715.394144-9-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

tests/qemu-iotests/297

@@ -95,6 +95,7 @@ def run_linters():
                             '--warn-redundant-casts',
                             '--warn-unused-ignores',
                             '--no-implicit-reexport',
+                            '--namespace-packages',
                             filename),
                            env=env,
                            check=False,