message: Fix type_is test
  Summary:
  More correct to check if function body is `ReturnTypeIs`.
  This is for the following diff.
diff: @@ -21,7 +21,10 @@ use crate as starlark;
  use crate::{
  assert::Assert,
  environment::GlobalsBuilder,
  - eval::compiler::def::{Def, FrozenDef},
  + eval::compiler::{
  + def::{Def, FrozenDef},
  + def_inline::InlineDefBody,
  + },
  values::{Value, ValueLike},
  };
  @@ -29,9 +32,15 @@ use crate::{
  fn globals(builder: &mut GlobalsBuilder) {
  fn returns_type_is<'v>(value: Value<'v>) -> anyhow::Result<bool> {
  Ok(if let Some(def) = value.downcast_ref::<FrozenDef>() {
  - def.def_info.inline_def_body.is_some()
  + matches!(
  + def.def_info.inline_def_body,
  + Some(InlineDefBody::ReturnTypeIs(..))
  + )
  } else if let Some(def) = value.downcast_ref::<Def>() {
  - def.def_info.inline_def_body.is_some()
  + matches!(
  + def.def_info.inline_def_body,
  + Some(InlineDefBody::ReturnTypeIs(..))
  + )
  } else {
  panic!("not def")
  })
  