Bad resolve with template async parameter

Blaze: `3.0.0` (`2.6.1` worked fine but no promise at that time)
Meteor: `3.0.2`

Since my migration of my application to Meteor 3.0, I figure out that some variable of template seems not to be resolve the way it used to be.

Here is an example :
```hbs

Content

```

If I use within blaze :
```hbs
{{#Test myProp=asyncProp}}
```

with :
```js
Template.XXX.helpers({
async asyncProp() {
return await something(); // return true
}
})
```

The template will always display `Dooh` instead of `Yeah`.
I expected once the resolve had been done, to pass the new value to the template so it can revaluate it and change the display accordingly.

Did I miss something there?

PS: [repo](https://github.com/DblK/meteor-blaze-inline-template) to reproduce the issue.

Start with the linked meteor-blaze-inline-template reproduction and the Template.XXX.helpers asyncProp example. Trace Blaze's template argument and conditional attribute handling for the async value, then verify that the class and conditional output update after the promise resolves.

Written by the indexing model from the issue text.