Slugify and python-slugify cannot coexist with new run_constrained

### Solution to issue cannot be found in the documentation.

- [X] I checked the documentation.

### Issue

Run: `conda install slugify python-slugify`. This returns an unsolvable environment specs error. This is likely because slugify is being pinned here to "less than version 0", but the only version of slugify that exists on conda-forge is 0.0.1. In fact, I don't even know how a "less than 0" pin even works.

@bollwyvl Can you check this out please? This is breaking lots of stuff.

### Installed packages

```shell
Base miniconda install on Windows, Python=3.10
```

### Environment info

```shell
Here's the releveant bits. Rest is censored:

conda version : 22.11.1
conda-build version : 3.23.3
python version : 3.10.8.final.0
virtual packages : __archspec=1=x86_64
__win=0=0
```
```