Fix: tests: create correct field class in bt_plugin_test_debug_info.py

Fix: tests: create correct field class in bt_plugin_test_debug_info.py

The wrong function is used to create this component class.  The
intention is to create a static array field class, but
create_dynamic_array_field_class is used.  Change it to
create_static_array_field_class.  Length 3 matches the length of the
value set in CompleteIter.__init__.

Change-Id: I69962e10c2f4b945487d7b818adcd71b460fe17b
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8327
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>