[BUG] `insert_mappings=false` not working

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

I have this configuration:
```
config = function()
require("toggleterm").setup({
open_mapping = [[t]],
start_in_insert = true,
-- terminal_mappings = true,
insert_mappings = false, -- whether or not the open mapping applies in insert mode
direction = "horizontal",
close_on_exit = true, -- close the terminal window when the process exits
})
end,
```
with leader being spacebar, when hitting spacebar to separate words it keeps waiting for the next key and only option it apears in `which key` is toggle term

### Expected Behavior

`insert_mappings=false` should prevent me from hitting `t` to close the terminal while writing

### Steps To Reproduce

1. Copy plugin configuration
2. Set spacebar as `leader`
3. Open terminal with `t]`
4. Hit spacebar

### Environment

```Markdown
- OS: Archlinux
- neovim version: 10.1
- Shell: Zsh
```

### Anything else?

_No response_