Update SDK to 18603.0.0

BUG=b/354251827
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I8fe5ff10c0a2ceba00e7f32a646c4e1414dc5c9c
Reviewed-on: https://cos-review.googlesource.com/c/cos/overlays/board-overlays/+/78419
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
diff --git a/overlay-amd64-host/prebuilt.conf b/overlay-amd64-host/prebuilt.conf
index 6f3482e..ad43fac 100644
--- a/overlay-amd64-host/prebuilt.conf
+++ b/overlay-amd64-host/prebuilt.conf
@@ -1,2 +1,2 @@
 
-FULL_BINHOST="gs://cos-prebuilt/117/18594.0.0/sdk"
+FULL_BINHOST="gs://cos-prebuilt/117/18603.0.0/sdk"