cmd/release: start running release tests for windows-arm64

By now, all outstanding issues preventing release tests for
windows-arm64 from being turned on by default are resolved:

- Issues golang/go#46406 and golang/go#46502 are fixed.
- The other remaining blocker golang/go#47017 is determined to be a
  builder-specific issue (not reproducible on physical Windows ARM64
  hardware) that by now happens infrequently enough that automated
  retries should be able to cover for future occurrences.
  Issue golang/go#47965 is opened to track progress on this.
- The builder performance is good and allows release tests to complete
  quickly, not adding any bottlenecks to the release process.

If something changes, we can revisit this, but information available
so far suggests it's a good time to start running release tests for
windows/arm64 by default.

Fixes golang/go#47017.
Updates golang/go#47965.

Change-Id: Ie96164821a2f8e795a22ac2d36b7292587a3e117
Reviewed-on: https://go-review.googlesource.com/c/build/+/345129
Reviewed-by: Alexander Rakoczy <alex@golang.org>
Trust: Dmitri Shuralyov <dmitshur@golang.org>

cmd/release/release.go

@@ -206,10 +206,6 @@ var builds = []*Build{
 		Arch:    "arm64",
 		Race:    false, // Not supported as of 2021-06-01.
 		Builder: "windows-arm64-10",
-		// TODO(golang.org/issue/46406, golang.org/issue/46502): Fix
-		// or skip failing tests, ensure the builder is fast enough to
-		// complete tests, then remove SkipTests here.
-		SkipTests: true,
 	},
 	{
 		GoQuery: ">= go1.17beta1",