MacroLiveSampleError if there is an embedlivesample macro before the first H2

[bsmth]

Failing:

<!-- ## Section heading -->

A para

```html live-sample___testing
<p>Hello world</p>
```

{{EmbedLiveSample("testing")}}

Passing

## Section heading

A para

```html live-sample___testing
<p>Hello world</p>
```

{{EmbedLiveSample("testing")}}

Steps to reproduce:

1. Add the contents from the failing case into a new post with any frontmatter
2. Run yarn build:blog

[bsmth]

Current workaround is to move the {{EmbedLiveSample("example-name")}} call after the first ## H2 heading or create a new H2 like ## Overview before the example.