Update RELEASE_R8_STORE_STORE_FENCE_CONSTRUCTOR_INLINING namespace

This updates the namespace of the build flag to the system_performance namespace to allow using Gantry.

Bug: 278964529
Change-Id: I1a3596dc685d74dd89715c05efef38216a11de43
Test: existing

flag_declarations/RELEASE_R8_STORE_STORE_FENCE_CONSTRUCTOR_INLINING.textproto

diff --git a/flag_declarations/RELEASE_R8_STORE_STORE_FENCE_CONSTRUCTOR_INLINING.textproto b/flag_declarations/RELEASE_R8_STORE_STORE_FENCE_CONSTRUCTOR_INLINING.textproto
index 4aa7524..580cb60 100644
--- a/flag_declarations/RELEASE_R8_STORE_STORE_FENCE_CONSTRUCTOR_INLINING.textproto
+++ b/flag_declarations/RELEASE_R8_STORE_STORE_FENCE_CONSTRUCTOR_INLINING.textproto
@@ -1,5 +1,5 @@
 name:  "RELEASE_R8_STORE_STORE_FENCE_CONSTRUCTOR_INLINING"
-namespace:  "android_UNKNOWN"
+namespace:  "system_performance"
 description:  "feature flag for enabling more aggressive constructor inlining in R8"
 workflow:  LAUNCH
 containers:  "product"