Error when combining `bind` and external command flag `<` in `TIG_SCRIPT`

I'm unable to use the `bind` command combined with `<` to exit tig after external command when using `TIG_SCRIPT`. Here is an example:

```console
$ TIG_SCRIPT=<(echo ':bind generic x <echo hello') tig
tig: Error reading script: Missing '>' from key mapping: <echo hello
```

The same `:bind generic x <echo hello` command works fine if executed from the tig ui.