When exporting example blocks from Org mode to Markdown, the language should not be "example" but omitted.

This is similar to #4748.

> cat test.org
#+BEGIN_EXAMPLE
Line 1
Line 2
#+END_EXAMPLE

> cat test.org | pandoc --from=org --to=markdown
``` example
Line 1
Line 2
```

Instead this should be converted to:

```
Line 1
Line 2
```

Pandoc version?
pandoc 3.8.3 on Ubuntu