The tag is present in Lintian version 2.109.3. That is the most recent version we know about.
This package appears to contain Python test files such as
test_foo/ in the global module
Whilst the tests may be useful in the binary package, it is probably a mistake to pollute the "top-level" namespace in this way.
Please install them to a subdirectory of the module being tested instead or simply omit from the binary package entirely.