tests: blacklist test-demandimport from test-check-module-imports

It just does too much weird import stuff to have a hope of passing the
checks.

tests/test-check-module-imports.t

@@ -28,6 +28,7 b' outputs, which should be fixed later.'
   > -X tests/hypothesishelpers.py \
   > -X tests/test-commit-interactive.t \
   > -X tests/test-contrib-check-code.t \
+  > -X tests/test-demandimport.py \
   > -X tests/test-extension.t \
   > -X tests/test-hghave.t \
   > -X tests/test-hgweb-auth.py \