Style check false positive on horizontal rule

A section separator (html: `

---

`) is created in sphinx with:

```

--------

```

That is: a line of a repeated single character (at least three... and I always use hyphens), surrounded by blank lines.

This is causing a false positive for `style-guide.check-label`

@ankita240796

Start at the style-guide.check-label check and reproduce it with the Sphinx section separator shown in the issue. Trace why a line of repeated hyphens between blank lines is reported, then verify that this horizontal rule no longer produces a false positive while other label violations still do.

Written by the indexing model from the issue text.