Add copyright to tests.

Change-Id: I8ea41675cf18007cb34aecfa43762a24fabd0d78
diff --git a/tests/verilator_sim/BUILD b/tests/verilator_sim/BUILD
index 6a87335..5c346cd 100644
--- a/tests/verilator_sim/BUILD
+++ b/tests/verilator_sim/BUILD
@@ -1,3 +1,5 @@
+# Copyright 2023 Google LLC
+
 cc_library(
     name = "sim_libs",
     hdrs = [