Update to a renaming in fenced frame spec, to fix build. (WICG#1261)

Co-authored-by: Maks Orlovich <morlovich@chromium.org>

spec.bs

@@ -854,12 +854,12 @@ To <dfn>construct a pending fenced frame config</dfn> given an [=auction config=
   : [=fenced frame config/on navigate callback=]
   :: null
 
-  : [=fenced frame config/effective sandbox flags=]
+  : [=fenced frame config/effective sandboxing flags=]
   :: a [=struct=] with the following [=struct/items=]:
-    : [=effective sandbox flags/value=]
+    : [=effective sandboxing flags/value=]
     :: TODO: fill this in once fenced frame sandbox flags are more fully specified
 
-    : [=effective sandbox flags/visibility=]
+    : [=effective sandboxing flags/visibility=]
     :: "<a for=visibility>`opaque`</a>"
 
   : [=fenced frame config/effective enabled permissions=]
@@ -1084,12 +1084,12 @@ To <dfn>create nested configs</dfn> given [=generated bid/ad component descripto
     : [=fenced frame config/on navigate callback=]
     :: null
 
-    : [=fenced frame config/effective sandbox flags=]
+    : [=fenced frame config/effective sandboxing flags=]
     :: a [=struct=] with the following [=struct/items=]:
-      : [=effective sandbox flags/value=]
+      : [=effective sandboxing flags/value=]
       :: TODO: fill this in once fenced frame sandbox flags are more fully specified
 
-      : [=effective sandbox flags/visibility=]
+      : [=effective sandboxing flags/visibility=]
       :: "<a for=visibility>`opaque`</a>"
 
     : [=fenced frame config/effective enabled permissions=]