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

• Parse optimisations go-git/go-git#602
• Optimise zlib reader and consolidate sync.Pools go-git/go-git#608

Upstream behaviour changes

• go-git/go-git: Surface a way for users to change unsupported capabilities.
  • Allow unsupported multi_ack capability go-git/go-git#613
• skeema/knownhosts and/or go-git/go-git: Add support for auto-populate HostKeyAlgorithms for non file-based knownhosts.
  • plumbing: transport/ssh, auto-populate HostKeyAlgorithms. Fixes #411 go-git/go-git#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:
    • Unable to use IUA due to server host key type flux2#1595
• Add support for env proxying when using HTTPS with custom CAs
  • add support for env proxying when using HTTPS with custom CAs go-git#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 go-git/go-git#655. The latter will require the upstreaming of fluxcd/go-git#9.