go/callgraph/rta: skip test on js platform

(Yesterday's CL 609576 added a dependency on packages.Load.)

Fixes golang/go#69299

Change-Id: Id858bbbb347ef137e053669b2fdef9522d057776
Reviewed-on: https://go-review.googlesource.com/c/tools/+/611576
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

go/callgraph/rta/rta_test.go

@@ -23,6 +23,7 @@ import (
 	"golang.org/x/tools/go/ssa"
 	"golang.org/x/tools/go/ssa/ssautil"
 	"golang.org/x/tools/internal/aliases"
+	"golang.org/x/tools/internal/testenv"
 	"golang.org/x/tools/internal/testfiles"
 	"golang.org/x/tools/txtar"
 )
@@ -85,6 +86,8 @@ func TestRTA(t *testing.T) {
 
 // loadPackages unpacks the archive to a temporary directory and loads all packages within it.
 func loadPackages(t *testing.T, archive string) []*packages.Package {
+	testenv.NeedsGoPackages(t)
+
 	ar, err := txtar.ParseFile(archive)
 	if err != nil {
 		t.Fatal(err)