kunit: tool: test: Don't rely on implicit working directory change

kunit: tool: test: Don't rely on implicit working directory change

If no kunitconfig_paths are passed to LinuxSourceTree() it falls back to
DEFAULT_KUNITCONFIG_PATH. This resolution only works when the current
working directory is the root of the source tree. This works by chance
when running the full testsuite through the default unittest runner, as
some tests will change the current working directory as a side-effect of
'kunit.main()'. When running a single testcase or using pytest, which
resets the working directory for each test, this assumption breaks.

Explicitly specify an empty kunitconfig for the affected tests.

Link: https://lore.kernel.org/r/20260107015936.2316047-2-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>