Error parsing relative path in `{glue}` role with subcommand

[rossbar]

Describe the bug

If I use the {glue} role with a specific subcommand (e.g. {glue:text}), I get a warning that the key is not found, even when the path is specified correctly. For example, this: {glue:text}demographics.md::num_respondents` gives the following warning:

WARNING: No key 'demographics.md:' found in glue data for this document. (use `path::key`, to glue from another document) [mystnb.glue] [mystnb.glue]

The structure of the warning to me implies that there is a problem with the parsing of colons here, as the demographics.md: part of the warning is very suspicious.

Indeed when I remove the :text subcommand from the {glue} directive, the warning disappears: {glue}demographics.md::num_respondents`.

Possibly related to #591

Reproduce the bug

For ease of reproduction, I recommend creating two new dummy files in the same directory of an existing myst-nb project:

1. Create foo.md with the following contents:

   
   ---                                                                             
   jupytext:                                                                       
   formats: md:myst                                                              
   text_representation:                                                          
   format_name: myst                                                           
   kernelspec:                                                                     
   display_name: Python 3                                                        
   name: python3                                                                 
   ---                                                                             

FOO

---                                                                             
tags: [hide-input]                                                              
---                                                                             
from myst_nb import glue                                                        
glue("answer", 42, display=False)                                               

2. Create `bar.md` with the following contents:

---

jupytext:
formats: md:myst
text_representation:
format_name: myst
kernelspec:
display_name: Python 3
name: python3

---

BAR

This line warns and fails to link: {glue:text}foo.md::answer.

This line is fine: {glue}foo.md::answer.

3. Add `foo` and `bar` to the toctree
4. Then build the project: `make html`. This should give the warning:

<path/to>/bar.md:13: WARNING: No key 'foo.md:' found in glue data for this document. (use path::key, to glue from another document) [mystnb.glue] [mystnb.glue]

### List your environment

I'm using myst-nb via sphinx directly without the jupyter-book CLI, so hopefully relevant info:

myst-nb 1.1.1 myst-parser 4.0.0 Sphinx 8.0.2

[bsipocz]

@rossbar - please open a PR once you've found a solution for this 😉