doc: develop: testing: Fix broken reference to pytest suite help

This should have been adapted directly with or after
v2021.01-693-gca6583d4e08 ("doc: move test/README to HTML
documentation") or v2021.01-694-g0157619d5c8 ("doc: move
test/py/README.md to HTML documentation") already.

Signed-off-by: Alexander Dahl <ada@thorsis.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
1 file changed