Update go-git dependencies to v5.4.x

[hiddeco]

The go-git dependency that we use in the flux binary and in multiple controllers has seen a new v5.4.0 minor release today, with updates we would likely benefit from:

• Submodele, fetch submodules pointing to orphaned but still reachable commits Fetch submodules pointing to orphaned but still reachable commits go-git/go-git#284 (edigaryev)
• plumbing: format/packfile, prevent large objects from being read into memory completely plumbing: format/packfile, prevent large objects from being read into memory completely go-git/go-git#303 (zeripath)
• plumbing: transport/ssh, support more formats in NewPublicKeys SSH helper plumbing: transport/ssh, support more formats in NewPublicKeys SSH helper go-git/go-git#298 (hiddeco)
• *: replace golang.org/x/crypto/openpgp by github.com/ProtonMail/go-crypto/openpgp Replace golang.org/x/crypto/openpgp by github.com/ProtonMail/go-crypto/openpgp go-git/go-git#283 (johanfleury)

To do:

• Update source-controller dependency, and implement NewPublicKeys helper as a replacement for Switch to crypto/ssh for parsing of private keys source-controller#339
• Update image-automation-controller dependency
• Update flux dependency, and implement NewPublicKeys helper as a replacement for Switch to crypto/ssh for parsing of private keys #1404