kunit: tool: test: Rename test_data_path() to _test_data_path()

kunit: tool: test: Rename test_data_path() to _test_data_path()

Running the KUnit testsuite through pytest fails, as the function
test_data_path() is recognized as a test function. Its execution fails
as pytest tries to resolve the 'path' argument as a fixture which does
not exist.

Rename the function, so the helper function is not incorrectly
recognized as a test function.

Link: https://lore.kernel.org/r/20260107015936.2316047-1-davidgow@google.com
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>