Add pw_status dep to to_string_test.

Change-Id: I6fd09f310b9d362551d05b0eb27192ecba808748
diff --git a/pw_string/BUILD b/pw_string/BUILD
index 9b9f29b..22e198b 100644
--- a/pw_string/BUILD
+++ b/pw_string/BUILD
@@ -55,5 +55,8 @@
 pw_cc_test(
     name = "to_string_test",
     srcs = ["to_string_test.cc"],
-    deps = ["//pw_string"],
+    deps = [
+        "//pw_status",
+        "//pw_string",
+    ],
 )