Pin cos/tools to master

BUG=b/539614585

Change-Id: I37c2a4b233cc0ca1f8c3c8b6d3a7f9970b52d60e
Reviewed-on: https://cos-review.googlesource.com/c/cos/manifest/+/176247
Tested-by: Chenglong Tang <chenglongtang@google.com>
Reviewed-by: Miri Amarilio <mirilio@google.com>

external_full.xml

diff --git a/external_full.xml b/external_full.xml
index f4490a1..46e955f 100644
--- a/external_full.xml
+++ b/external_full.xml
@@ -236,7 +236,7 @@
 
   <project path="src/cos_tools"
            name="cos/tools"
-           revision="refs/heads/release-R133" />
+           revision="refs/heads/master" />
   <project path="src/platform/cobble"
            name="cos/cobble" />
   <project path="manifest" name="cos/manifest" >