use our java tests target instead of recursive walk (#8777)

diff --git a/kokoro/linux/bazel/build.sh b/kokoro/linux/bazel/build.sh
index c46a5dd..300e212 100755
--- a/kokoro/linux/bazel/build.sh
+++ b/kokoro/linux/bazel/build.sh
@@ -25,7 +25,7 @@
 trap print_test_logs EXIT
 bazel test --copt=-Werror --host_copt=-Werror \
   //:build_files_updated_unittest \
-  //java/... \
+  //java:tests \
   //:protoc \
   //:protobuf \
   //:protobuf_python \