cmd/makemac: update darwin-amd64-12

This should address darwin-amd64-12 bot availability issues.

Change-Id: I6a6a636c36949f8bf01fecb03be98285c279cfce
Reviewed-on: https://go-review.googlesource.com/c/build/+/750800
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>

cmd/makemac/config.go

diff --git a/cmd/makemac/config.go b/cmd/makemac/config.go
index d685323..66a1607 100644
--- a/cmd/makemac/config.go
+++ b/cmd/makemac/config.go
@@ -60,7 +60,7 @@
 			Hostname: "darwin-amd64-12",
 			Cert:     "secret:symbolic-datum-552/darwin-amd64-12-cert",
 			Key:      "secret:symbolic-datum-552/darwin-amd64-12-key",
-			Image:    "63771f3f8c869197fdff27c7357adc3a03f88e94c2493c0bb67d2a748eaed34e",
+			Image:    "f48c5538d2ac7b91c592dcce18f247e3aad70503558f92b41bdc010f2c8728a9",
 			Count:    5, // Fewer because it runs on release branches only.
 		},
 		{
@@ -99,7 +99,7 @@
 			Hostname: "darwin-amd64-12-security",
 			Cert:     "secret:symbolic-datum-552/darwin-amd64-12-security-cert",
 			Key:      "secret:symbolic-datum-552/darwin-amd64-12-security-key",
-			Image:    "63771f3f8c869197fdff27c7357adc3a03f88e94c2493c0bb67d2a748eaed34e",
+			Image:    "f48c5538d2ac7b91c592dcce18f247e3aad70503558f92b41bdc010f2c8728a9",
 			Count:    4,
 		},
 		{