Roll gallery to b6728704a6441ac37a21e433a1e43c990780d47b (#114537)

Author: cbracken

dev/devicelab/lib/versions/gallery.dart

@@ -3,4 +3,4 @@
 // found in the LICENSE file.
 
 /// The pinned version of flutter gallery, used for devicelab tests.
-const String galleryVersion = '9fd4ee5cb2d280f4ddb497e17acf404cb78c96f6';
+const String galleryVersion = 'b6728704a6441ac37a21e433a1e43c990780d47b';