Table labels with attributes don't render correctly

Hello,

It seems that attributes in table labels are only substituted in the rendered list of tables. The attribute in the actual table label is not substituted. Is this a known limitation, or a bug?

Steps to reproduce:

example.adoc
```
= Title

:MyAttribute: MyValue

My Attribute is {MyAttribute}.

[width="100%",options=header,cols="30,10"]
.{MyAttribute} in a table label
|===
|Heading 1 |Heading 2
|Entry 1 |Entry 2
|===

== List of Tables

list-of::table[]
```

```
asciidoctor-pdf -r asciidoctor-lists example.adoc
```