Dependabot - Private "Registries"/"Dependencies"/"Repositories" is misleading

### Code of Conduct

- [x] I have read and agree to the GitHub Docs project's [Code of Conduct](https://github.com/github/docs/blob/main/.github/CODE_OF_CONDUCT.md)

### What article on docs.github.com is affected?

https://docs.github.com/en/code-security/reference/supply-chain-security/supported-ecosystems-and-repositories

### What part(s) of the article would you like to see updated?

Dependabot sometimes cannot resolve private dependencies for some ecosystems (e.g. Nix, currently)

However, this is expressed in 3 different expressions:
1. Private **Registries**
2. Private **Dependencies**
3. Private **Repositories**

Those can be misleading

For example:
I personally thought dependabot was completely not working for some ecosystems independently of private dependencies when the `dependabot.yml` file was inside of a private repository

Harmonizing the "Private *" term with a single word (probably "Private Dependencies", since it encompasses both registries and repositories) would have cleared up any confusion

### Additional information

_No response_

Leia o artigo afetado em docs.github.com/en/code-security/reference/supply-chain-security/supported-ecosystems-and-repositories, concentrando-se nas três ocorrências de “Private Registries”, “Private Dependencies” e “Private Repositories”. Harmonize a terminologia para que o escopo das dependências e dos repositórios privados fique claro e, em seguida, revise o artigo renderizado para verificar a consistência da redação.

Escrita pelo modelo de indexação a partir do texto da issue.