eclass-overlay: Add crosvm to cups-proxy group

The Plugin VM needs access to the CUPS proxy socket, so let's add it to the
cups proxy group.

BUG=b:117218264
TEST=Build and boot

Cq-Depend: chromium:1761768
Change-Id: I7cb24135fb9e631faeb46d5d87cd539859ade191
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/eclass-overlay/+/1761632
Tested-by: Dmitry Torokhov <dtor@chromium.org>
Auto-Submit: Dmitry Torokhov <dtor@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
diff --git a/profiles/base/accounts/group/cups-proxy b/profiles/base/accounts/group/cups-proxy
index 0af4553..bf98bc5 100644
--- a/profiles/base/accounts/group/cups-proxy
+++ b/profiles/base/accounts/group/cups-proxy
@@ -1,3 +1,4 @@
 group:cups-proxy
 gid:20136
-users:cups-proxy
+# VMs run as crosvm user
+users:crosvm,cups-proxy