Fix ambiguous phrasing in tests comments regarding $opt$.

Change-Id: I78e6bccbe35288df5de30700d3877bbcdef37d65
diff --git a/test/404-optimizing-allocator/src/Main.java b/test/404-optimizing-allocator/src/Main.java
index 7b31820..1ff5475 100644
--- a/test/404-optimizing-allocator/src/Main.java
+++ b/test/404-optimizing-allocator/src/Main.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-// Note that $opt$reg$ is a marker for the optimizing compiler to ensure
+// Note that $opt$reg$ is a marker for the optimizing compiler to test
 // it does use its register allocator.
 
 public class Main {