acctest: fix datasource's image name

As already committed on main, this fixes one acceptance test before
releasing v1.9.5 so we make sure tests are working.

acctest/plugin/test-fixtures/basic-amazon-ami-datasource.pkr.hcl

@@ -9,7 +9,7 @@ packer {
 
 data "amazon-ami" "test" {
   filters = {
-    name                = "ubuntu/images/*ubuntu-xenial-16.04-amd64-server-*"
+    name                = "ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*"
     root-device-type    = "ebs"
     virtualization-type = "hvm"
   }
@@ -25,6 +25,7 @@ source "amazon-ebs" "basic-example" {
   communicator  = "ssh"
   instance_type = "t2.micro"
   ssh_username  = "ubuntu"
+  skip_create_ami = true
 }
 
 build {