Correct syntax highlighting for inline LaTeX

[user202729]

Pandoc has the feature

```{=latex}
code...
```

to embed LaTeX.

However currently it's not possible to highlight the code inside correctly

let g:pandoc#syntax#codeblocks#embeds#langs = [
			\ "latex=tex",
			\ "{=latex}=tex",  " <--- this does not work
			\ "python",
			\ ]