[Instrumented libraries] Switch default release to Focal

This should be a no-op on the bots since they manually specify
`instrumented_libraries_release`.  This change is mainly for gLinux,
where devs are having issues using the Xenial instrumented libraries
due to having different versions of dependencies (eg. libnettle.so.6).

R=thestig

Change-Id: Ic3aa74da1034c7c6b2826a7acb73a57bd3bcf393
Bug: 1260217, 1334390
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4074160
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1079527}
NOKEYCHECK=True
GitOrigin-RevId: a9feccefae2bdbe891fcee1d7f3783d91f43cba6
diff --git a/BUILD.gn b/BUILD.gn
index f7f3ad7..7cb109f 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -5,7 +5,7 @@
 import("//build/config/sanitizers/sanitizers.gni")
 
 declare_args() {
-  instrumented_libraries_release = "xenial"
+  instrumented_libraries_release = "focal"
 }
 
 group("deps") {