[False Positive] `# <Word> To-Do` is flagged as not title case & code action gives wrong suggestion

**What got flagged?**
Line:
```markdown
## Daily To-Do

```
**Diagnostic on that line:**
Try to use title case in headings.

The code action also gives wrong suggestion.

Just adding `# Todo` as heading doesn't the trigger the warning. Only when an additional word is added to the heading, it flags the heading not been title case.

**Additional Information**

nvim-lspconfig:
```lua
harper_ls = {
enabled = true,
filetypes = { 'markdown'},
settings = {
['harper-ls'] = {
userDictPath = '~/.config/nvim/spell/en.utf-8.add',
-- linters = {
-- -- ToDoHyphen = false,
-- -- SentenceCapitalization = true,
-- -- SpellCheck = true,
-- },
isolateEnglish = true,
markdown = {
IgnoreLinkTitle = true,
},
},
},
},

```

Reproduce the diagnostic and code action on the Markdown heading `## Daily To-Do`, using the nvim-lspconfig setup shown in the issue. Start by tracing the title-case check and its suggestion for headings with `To-Do`; done means this heading is not falsely flagged and the code action no longer suggests the wrong replacement.

Written by the indexing model from the issue text.