cmd/fiximports: skip TestFixImports on plan9-arm

For golang/go#50775.

Change-Id: Ia7d99e9e7b007af3fa35332f0385949867e975eb
Reviewed-on: https://go-review.googlesource.com/c/tools/+/398817
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>

cmd/fiximports/main_test.go

@@ -55,6 +55,9 @@ func init() {
 }
 
 func TestFixImports(t *testing.T) {
+	if os.Getenv("GO_BUILDER_NAME") == "plan9-arm" {
+		t.Skipf("skipping test that times out on plan9-arm; see https://go.dev/issue/50775")
+	}
 	testenv.NeedsTool(t, "go")
 
 	defer func() {