dashboard: reduce GOMAXPROCS on Windows 11 ARM64

The Windows 11 ARM64 builder is experiencing occasional OOMs while
building tests. Reducing GOMAXPROCS will reduce the go command's
parallelism and hopefully prevent them.

For golang/go#51019.

Change-Id: Ia4bfdddaca178c130b9b57087a66a54cff903a05
Reviewed-on: https://go-review.googlesource.com/c/build/+/385182
Trust: Heschi Kreinick <[email protected]>
Run-TryBot: Heschi Kreinick <[email protected]>
Auto-Submit: Heschi Kreinick <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: heschi

dashboard/builders.go

@@ -2262,6 +2262,7 @@ func init() {
 		},
 		env: []string{
 			"GOARCH=arm64",
+			"GOMAXPROCS=4", // OOM problems, see go.dev/issue/51019
 		},
 	})
 	addBuilder(BuildConfig{