Improve Git Credential Helper Detection for Linux (GCM & libsecret support) (#3264)
* feat: add support for Git Credential Manager (GCM)
- Update GIT_CREDENTIAL_REGEX to match git-credential-manager
- Add tests to verify GCM is recognized and handled
Ref: https://git-scm.com/doc/credential-helpers
* feat: support for git-credential-libsecret in credential helper detection
- Extend GIT_CREDENTIAL_REGEX to recognize git-credential-libsecret, enabling integration with Secret Service-compatible keyrings (e.g., GNOME Keyring, KDE Wallet) on Linux.
- Add unit tests to validate detection and handling of git-credential-libsecret
Ref: https://git-scm.com/doc/credential-helpers
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Co-authored-by: Lucain <lucain@huggingface.co>