git: Requirements to move back to `go-git/go-git`

[pjbgf]

The go-git/go-git dependency has recently been replaced with fluxcd/go-git`. In order to be able to move back to the upstream project, we need:

Upstream performance improvements

• https://github.com/go-git/go-git/pull/602
• https://github.com/go-git/go-git/pull/608

Upstream behaviour changes

• [x] go-git/go-git: Surface a way for users to change unsupported capabilities.
  • https://github.com/go-git/go-git/pull/613
• [x] skeema/knownhosts and/or go-git/go-git: Add support for auto-populate HostKeyAlgorithms for non file-based knownhosts.
  • https://github.com/go-git/go-git/pull/548 broke backwards compatibility. fluxcd/go-git reverts some of its changes so that the latest versions of go-git/go-git continue to work with Flux.
  • The auto-population of HostKeyAlgorithms is a great feature to have and will decrease the likelihood of issues such as:
  • https://github.com/fluxcd/flux2/issues/1595
• [x] Add support for env proxying when using HTTPS with custom CAs
  • https://github.com/fluxcd/go-git/pull/9

[pjbgf]

Runnign the tests using upstream go-git version (v5.6.0) breaks two tests:

1. Test_SOCKS5_proxy
2. Test_HTTP_proxy/env_var:_HTTPS_PROXY

The former is fixed by https://github.com/go-git/go-git/pull/655. The latter will require the upstreaming of https://github.com/fluxcd/go-git/pull/9.