cmd/gomobile: skip TestWriter

TestWriter is flaky and often fails on the trybots. Skip this as a
tentative solution.

Updates golang/go#40290

Change-Id: I3a8aa74fb6cb727a216da4046edaa159f9aa2dc3
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/243839
Run-TryBot: Hajime Hoshi <hajimehoshi@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

Author: hajimehoshi

cmd/gomobile/writer_test.go

@@ -15,6 +15,10 @@ import (
 )
 
 func TestWriter(t *testing.T) {
+	if os.Getenv("GO_BUILDER_NAME") == "linux-amd64-androidemu" {
+		t.Skip("skipping on linux-amd64-androidemu builder; see golang.org/issue/40290")
+	}
+
 	block, _ := pem.Decode([]byte(debugCert))
 	if block == nil {
 		t.Fatal("no cert")