Dependencies doesn't error with wrong right hand side

[wolfv]

Checks

• [X] I have checked that this issue has not already been reported.

• [X] I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

I accidentally had

[dependencies]
dependencies = { pillow = "*" }

in my pixi.toml

Issue description

pixi tried to resolve * as a name I think and then complained about not finding a matching package.

Expected behavior

Ideally we'd see that this doesn't make sense and give a helpful error message that says {pillow = "*"} is not a valid matchspec.