r/aws_appstream_fleet: handle ResourceNotFound during stop fleet

During destroy the StopFleet operation was not handling ResourceNotFound exceptions. This change will capture these errors and proceed with removing the resource from state as nothing further is required to delete the resource.

internal/service/appstream/fleet.go

@@ -525,6 +525,9 @@ func resourceFleetDelete(ctx context.Context, d *schema.ResourceData, meta inter
 	_, err := conn.StopFleetWithContext(ctx, &appstream.StopFleetInput{
 		Name: aws.String(d.Id()),
 	})
+	if tfawserr.ErrCodeEquals(err, appstream.ErrCodeResourceNotFoundException) {
+		return diags
+	}
 	if err != nil {
 		return sdkdiag.AppendErrorf(diags, "stopping Appstream Fleet (%s): %s", d.Id(), err)
 	}