fix: update named arg schema

[bollwyvl]

references

• follow-on to feat(tasks): named args in depends-on #4148
• continues Allow named args in depends-on #3536

changes

• update args schema to reflect current reading
• add TaskArgName with regex for arg names
• update task_arguments_dependent.toml example to exercise/document more features

questions

• the task arg name regular expression needs a look
  • i don't think minijinja vars can start with numbers
  • i don't know about full unicode, could get hairy

[bollwyvl]

Could add some more invalid fixtures, I suppose, but otherwise this seems ready to review.

[lucascolley]

thanks @bollwyvl, LGTM!

the task arg name regular expression needs a look
i don't think minijinja vars can start with numbers
i don't know about full unicode, could get hairy

I'm not too worried about getting this 100% perfect, I think we should just merge this and iterate :)