dashboard: increase host-darwin-amd64-12-aws count

The current macstadium count is 5, but it is tricky to support an odd
number with our current setup on AWS (2 VMs per host), so use 6 instead.

For golang/go#48945.

Change-Id: Id00ccfcde3033722715a0299cf4f40acf1665c36
Reviewed-on: https://go-review.googlesource.com/c/build/+/432396
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Jenny Rakoczy <jenny@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 96183b5..928b59a 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -164,7 +164,7 @@
 	},
 	"host-darwin-amd64-12-aws": {
 		IsReverse:       true,
-		ExpectNum:       2,
+		ExpectNum:       6,
 		Notes:           "AWS macOS Monterey (12) VM under QEMU",
 		SSHUsername:     "gopher",
 		HermeticReverse: true, // we destroy the VM when done & recreate