[interop] Add grpc-java 1.64.0 to client_matrix.py (#36627)

Closes #36627

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36627 from temawi:client-matrix-java-1.64.0 3ac1c0b9c6
PiperOrigin-RevId: 634427373

tools/interop_matrix/client_matrix.py

@@ -442,6 +442,7 @@ LANG_RELEASE_MATRIX = {
             ("v1.60.1", ReleaseInfo()),
             ("v1.61.0", ReleaseInfo()),
             ("v1.63.0", ReleaseInfo()),
+            ("v1.64.0", ReleaseInfo()),
         ]
     ),
     "python": OrderedDict(