Parse error for Haskell sections

Consider the program:

```
main = print $ (`div` 2) 3
```

If you put the cursor inside the brackets anywhere *except* on the first back-tick character and hit `C-M-u` (`backward-up-list`) the cursor is placed at the beginning of the current buffer and a scan error is echoed to the `*Messages*` buffer:

```
up-list: Scan error: "Unbalanced parentheses", 1, 1
```

I tried to debug this, but I'm not great with lisp. I *think* it has to do with the fact that "plain" `backward-sexp` and `haskell-backward-sexp` don't agree on where to go when cursor is on the `d` in `div`. There is a comment in `haskell-forward-sexp` saying that:

> Navigate backwards using plain `backward-sexp', assume that it skipped over at least one Haskell expression

If I switch to `fundamental-mode` I can see that this assumption doesn't hold if you call `backward-sexp` with the cursor on the `d` in `div`.

I would love to provide the patch, but I'm afraid I need help digging to locate the bug.

The bug is present in at least versions 20231115.1812 and 20240116.1718.

Reproduce the example in haskell-mode and start by reading haskell-forward-sexp, haskell-backward-sexp, and the interaction with plain backward-sexp at the d in div. Done means C-M-u correctly navigates from every position inside the Haskell section without reporting an unbalanced-parentheses scan error.

Written by the indexing model from the issue text.