Update Security String to 2021-08-05 am: f5139e3087

Original change: https://googleplex-android-review.googlesource.com/c/platform/build/+/14966269

Change-Id: I5766ee11c2b1717f0aedd4895ce01108687c7d6c
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 13b85c0..f900f89 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -240,7 +240,7 @@
     #  It must be of the form "YYYY-MM-DD" on production devices.
     #  It must match one of the Android Security Patch Level strings of the Public Security Bulletins.
     #  If there is no $PLATFORM_SECURITY_PATCH set, keep it empty.
-      PLATFORM_SECURITY_PATCH := 2021-07-05
+      PLATFORM_SECURITY_PATCH := 2021-08-05
 endif
 .KATI_READONLY := PLATFORM_SECURITY_PATCH