Only run cross-platform tests to avoid running jj or rr twice

Author: kegsay

.github/workflows/tests.yaml

@@ -155,6 +155,7 @@ jobs:
           COMPLEMENT_BASE_IMAGE: homeserver
           COMPLEMENT_ENABLE_DIRTY_RUNS: 1
           COMPLEMENT_CRYPTO_MITMDUMP: mitm.dump
+          COMPLEMENT_CRYPTO_TEST_CLIENT_MATRIX: jr,rj
           COMPLEMENT_SHARE_ENV_PREFIX: PASS_
           PASS_SYNAPSE_COMPLEMENT_DATABASE: sqlite
           DOCKER_BUILDKIT: 1