text: Title: RFE: Prefer TOML-native configuration over legaci INI
  Body: ## What's the problem this feature will solve?
  
   - I want old tox versions to know I need tox \>= 4.21
   - I want to use TOML-native configuration
  
  If I have this:
  
  ```toml
  [tool.tox]
  requires = ["tox>=4.21"]
  env_list = ["3.13", "3.12", "type", "doc"]
  ...
  ```
  
  The old tox does not read it and ignores it.
  
  If I change it like this:
  
  ```toml
  [tool.tox]
  legacy_tox_ini = """
      [tox]
      min_version = 4.21
  """
  env_list = ["3.13", "3.12", "type", "doc"]
  ...
  ```
  
  The old tox reads it and updates tox in the provision venv.
  However, the TOML-native configuration is ignored by the new tox.
  
  ## Describe the solution you'd like
  
  I believe this could be solved if the new tox preferred the TOML-native configuration over legacy_tox_ini if both exist.
  
  ## Alternative Solutions
  
  I could stick with legacy_tox_ini unless I know all environments are fully updated to tox > 4.21.
  
  Thanks