Increase the size of the image to 6GB.

Bug: 371491254
Change-Id: I38cc16858abd99f4484383854b4802112caafa91
Test: build
diff --git a/build/debian/image.yaml b/build/debian/image.yaml
index eb42a07..93ec273 100644
--- a/build/debian/image.yaml
+++ b/build/debian/image.yaml
@@ -46,7 +46,7 @@
 vendors:
 - name: nocloud
   faiClasses: [SYSTEM_BOOT, NOCLOUD, LINUX_VARIANT_BASE, TIME_SYSTEMD, AVF]
-  size: 2
+  size: 6
 
 types:
 - name: dev