cmd/go: add darwin/arm64 in the list of supported systems in help message

Fixes #49173.

Change-Id: I71270b4ff7e9ede3cdfa5946b73142a731752adf
Reviewed-on: https://go-review.googlesource.com/c/go/+/358901
Reviewed-by: Alberto Donizetti <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Trust: Alberto Donizetti <[email protected]>
Run-TryBot: Alberto Donizetti <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: choleraehyq

src/cmd/go/alldocs.go

@@ -68,7 +68,7 @@ and test commands:
 		The default is GOMAXPROCS, normally the number of CPUs available.
 	-race
 		enable data race detection.
-		Supported only on linux/amd64, freebsd/amd64, darwin/amd64, windows/amd64,
+		Supported only on linux/amd64, freebsd/amd64, darwin/amd64, darwin/arm64, windows/amd64,
 		linux/ppc64le and linux/arm64 (only for 48-bit VMA).
 	-msan
 		enable interoperation with memory sanitizer.