fix: bug where couldn't put contracts_folder in dependency config_override config

[antazoey]

What I did

dependencies let you specify contracts_folder as a key but also offer a config_override.
however, when putting contracts_folder in config_override (which should be valid because contracts_folder is also a project's top-level config item), it fails with got multiple args for keyword 'contracts_folder', so this fixes that.

How I did it

check if contracts_folder is in config override. if no, then put the one you were gonna put else, leave it be.

How to verify it

dependencies:
  - name: solmate
    github: transmissions11/solmate
    ref: "v6"
    #contracts_folder: src
    config_override:
      contracts_folder: src
      compile:
        exclude: 
          - ./test/utils/*

run ape pm compile

Checklist

• All changes are completed
• New test cases have been added
• Documentation has been updated