kunit: test: Log the correct filter string in executor_test

KUnit's executor_test logs the filter string in KUNIT_ASSERT_EQ_MSG(),
but passed a random character from the filter, rather than the whole
string.

This was found by annotating KUNIT_ASSERT_EQ_MSG() to let gcc validate
the format string.

Fixes: 76066f93 ("kunit: add tests for filtering attributes")
Signed-off-by: David Gow <davidgow@google.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: Rae Moar <rmoar@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>