builders: redirect windows-386 slowbot alias to 2016 vintage

Update the "windows-386" slowbot alias to windows-386-2016
from windows-386-2008.

Updates golang/go#58007.

Change-Id: I44e10500fcf0520976a80916b1fc4a42307cd7a3
Reviewed-on: https://go-review.googlesource.com/c/build/+/470715
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

dashboard/builders.go

@@ -97,7 +97,7 @@ var slowBotAliases = map[string]string{
 	"solaris-amd64":         "solaris-amd64-oraclerel",
 	"wasm":                  "js-wasm-node18",
 	"windows":               "windows-amd64-2016",
-	"windows-386":           "windows-386-2008",
+	"windows-386":           "windows-386-2016",
 	"windows-amd64":         "windows-amd64-2016",
 	"windows-arm":           "windows-arm-zx2c4",
 	"windows-arm64":         "windows-arm64-11",