cmd/releasebot: simplify darwin-arm64 build definition

We don't make Go 1.15 minor releases by now, so including the
darwin-arm64 build "for Go 1.16 Beta 1 and newer" is the same
as always including it.

Also update test coverage that the list of builds for Go 1.18
is the same as Go 1.17, as expected.

Change-Id: If89a25e8179de48a2c2fabe78248897a67785416
Reviewed-on: https://go-review.googlesource.com/c/build/+/368414
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

cmd/releasebot/main.go

@@ -60,7 +60,7 @@ var releaseTargets = []Target{
 	{Name: "windows-amd64"},
 	{Name: "windows-arm64", GoQuery: ">= go1.17beta1"},
 	{Name: "darwin-amd64"},
-	{Name: "darwin-arm64", GoQuery: ">= go1.16beta1"},
+	{Name: "darwin-arm64"},
 	{Name: "linux-s390x"},
 	{Name: "linux-ppc64le"},
 
@@ -1055,9 +1055,7 @@ func match(query, goVer string) bool {
 	case "": // A special case to make the zero Target.GoQuery value useful.
 		return true
 	case ">= go1.17beta1":
-		return !strings.HasPrefix(goVer, "go1.16") && !strings.HasPrefix(goVer, "go1.15")
-	case ">= go1.16beta1":
-		return !strings.HasPrefix(goVer, "go1.15")
+		return !strings.HasPrefix(goVer, "go1.16")
 	default:
 		panic(fmt.Errorf("match: query %q is not supported", query))
 	}

cmd/releasebot/main_test.go

@@ -24,6 +24,7 @@ func TestTargetSelectionPerGoVersion(t *testing.T) {
 	}{
 		{
 			goVer: []string{
+				"go1.18beta1", "go1.18rc1", "go1.18", "go1.18.1",
 				"go1.17beta1", "go1.17rc1", "go1.17", "go1.17.1",
 			},
 			want: []string{
@@ -69,26 +70,6 @@ func TestTargetSelectionPerGoVersion(t *testing.T) {
 				"windows-amd64-longtest",
 			},
 		},
-		{
-			goVer: []string{"go1.15.11"},
-			want: []string{
-				"src",
-				"linux-386",
-				"linux-armv6l",
-				"linux-amd64",
-				"linux-arm64",
-				"freebsd-386",
-				"freebsd-amd64",
-				"windows-386",
-				"windows-amd64",
-				"darwin-amd64",
-				"linux-s390x",
-				"linux-ppc64le",
-				"linux-386-longtest",
-				"linux-amd64-longtest",
-				"windows-amd64-longtest",
-			},
-		},
 	} {
 		for _, goVer := range tc.goVer {
 			t.Run(goVer, func(t *testing.T) {