skip doctype as one possible fix for failure

==> Testing HTML::Parser::XML
t/01_basic.t ........ Invocant requires a type object, but an object instance was passed
  in method ACCEPTS at src/gen/m-CORE.setting:865
  in block  at lib/HTML/Parser/XML.pm6:85
  in block  at lib/HTML/Parser/XML.pm6:80
  in method parse at lib/HTML/Parser/XML.pm6:55
  in block <unit> at t/01_basic.t:9