MINOR: fix streams_broker_compatibility test (#16015)

The system test was broken in ccf4bd5
which failed to import the matrix symbol. The test was failing silently, not
discovering any tests.

Reviewers: Bruno Cadonna <cadonna@apache.org>

tests/kafkatest/tests/streams/streams_broker_compatibility_test.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 from ducktape.mark import parametrize
+from ducktape.mark import matrix
 from ducktape.mark.resource import cluster
 from ducktape.tests.test import Test
 from ducktape.utils.util import wait_until