Decrease worker count on internal bot

We saw os OOM kill of java

Change-Id: I7cad851b380fec973f7e47caad5d7d48e2166579
diff --git a/tools/internal_test.py b/tools/internal_test.py
index ade752c..f0bdf4b 100755
--- a/tools/internal_test.py
+++ b/tools/internal_test.py
@@ -117,7 +117,7 @@
         '--java_max_memory_size=8G'
     ],
     # Ensure that all internal apps compile.
-    ['tools/run_on_app.py', '--run-all', '--out=out', '--workers', '4'],
+    ['tools/run_on_app.py', '--run-all', '--out=out', '--workers', '3'],
 ]
 
 # Command timeout, in seconds.