Vendoring files should use config.toml instead of .cargo/config

[13hannes11]

When running a build using flatpak-builder I noticed the following message:

warning: /run/build/toolbox-tuner/.cargo/config is deprecated in favor of config.toml
note: if you need to support cargo 1.38 or earlier, you can symlink config to config.toml

To reproduce use:
this repository:
https://github.com/13hannes11/flathub/tree/org.kuchelmeister.ToolboxTuner

Vendoring is done in:
https://github.com/13hannes11/toolbox-tuner

[AaronErhardt]

Thanks for pointing this out. FYI I want to replace relm4-template with CLI that keeps all configs up-to-date, which should be long before cargo stops accepting the deprecated file path, so I likely won't invest many resources into this.