Replace redundant globbing in package data section in `pyproject.toml`

This is my bad, I think when I first tackled the `pyproject.toml` amidst the conda package build work I wasn't confident in how to handle the YAML file copying... :sweat_smile:

That being said, the following globbing https://github.com/DiamondLightSource/httomo/blob/7efb32b61436ea3711a2ff0d5bd1159777dab46e/pyproject.toml#L15-L17

can likely be replaced by a single line
```
"methods_database/packages/external/*/*.yaml"
```

to get the YAML files for all backend dirs (tomopy, httomolib, httomolibgpu).