Add Java 1.9.0 release to client_matrix.py
diff --git a/tools/interop_matrix/client_matrix.py b/tools/interop_matrix/client_matrix.py
index 71d3a79..7dbd07a 100644
--- a/tools/interop_matrix/client_matrix.py
+++ b/tools/interop_matrix/client_matrix.py
@@ -132,6 +132,9 @@
         {
             'v1.8.0': None
         },
+        {
+            'v1.9.0': None
+        },
     ],
     'python': [
         {