yew-macro: fix inability to set the autoplay attribute

[bakape]

Description

Fixes regression introduced in v0.17.4 -> v0.18.0, whereby you can no longer set the autoplay attribute, as it requires a boolean value but expands into a call to PositionalAttr::new() instead of PositionalAttr::new_boolean(), resulting in the following error:

autoplay=true
         ^^^^ the trait `IntoPropValue<std::option::Option<Cow<'static, str>>>` is not implemented for `bool`

After this passes, I will check if master is affected and merge + PR, if needed.

Checklist

• I have run cargo make pr-flow (test fail even on unmodified v0.18 for me; lets see what the CI will say)
• I have reviewed my own code
• I have added tests (extended one)

[bakape]

Only nightly tests failed, so seems to be fine.