Fix parentheses in //src/test/docker:BUILD

This was resulting in all the test having no tag or having the manual tag so no test was executed on ci.bazel.io.

PiperOrigin-RevId: 167831686
diff --git a/src/test/docker/BUILD b/src/test/docker/BUILD
index cf01798..195c3fa 100644
--- a/src/test/docker/BUILD
+++ b/src/test/docker/BUILD
@@ -50,12 +50,12 @@
         ],
         local = 1,
         main = "docker_test.py",
-        tags = ([
+        tags = [
             "docker",
             "exclusive",
             "local",
             "shard-%s" % SHARD_NUMBER[mode],
-        ] + ["manual"]) if (flavour == "debian-stretch") else [],
+        ] + (["manual"] if (flavour == "debian-stretch") else []),
         deps = ["//third_party/py/gflags"],
     ) for mode in SHARD_NUMBER]
     for flavour in FLAVOURS