Documentation: kunit: Correct MODULE_IMPORT_NS() syntax

The argument should be the string "EXPORTED_FOR_KUNIT_TESTING", not a
bare identifier.

Link: https://lore.kernel.org/r/20250616211637.111358-1-briannorris@chromium.org
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: computersforpeace

Documentation/dev-tools/kunit/usage.rst

@@ -699,7 +699,7 @@ the template below.
 	#include <kunit/visibility.h>
 	#include <my_file.h>
 	...
-	MODULE_IMPORT_NS(EXPORTED_FOR_KUNIT_TESTING);
+	MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");
 	...
 	// Use do_interesting_thing() in tests