build: Update go-git

[go-git-renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
github.com/go-git/go-billy/v6	v6.0.0-20260328065524-593ae452e14d → v6.0.0-20260410103409-85b6241850b5
github.com/go-git/go-git-fixtures/v6	v6.0.0-20260403205623-487c094a2af5 → v6.0.0-20260410103352-fe4fd2baf1dc
github.com/go-git/go-git/v6	v6.0.0-20260114124804-a8db3a6585a6 → v6.0.0-alpha.1

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This PR has been generated by Renovate Bot.

[go-git-renovate]

ℹ️ Artifact update notice

File name: go.mod

In order to perform the update(s) described in the table above, Renovate ran the go get command, which resulted in the following additional change(s):

• 3 additional dependencies were updated

Details:

Package	Change
github.com/ProtonMail/go-crypto	v1.3.0 -> v1.4.1
github.com/cloudflare/circl	v1.6.1 -> v1.6.3
github.com/kevinburke/ssh_config	v1.4.0 -> v1.6.0

[pjbgf]

@copilot fix the compilation issue due to change in the API:

Error: cmd/gogit/verify-pack.go:84:28: not enough arguments in call to idxfile.NewDecoder
have (billy.File)
want (io.Reader, "github.com/go-git/go-git/v6/plumbing/hash".Hash)

[Copilot]

@copilot fix the compilation issue due to change in the API:

Error: cmd/gogit/verify-pack.go:84:28: not enough arguments in call to idxfile.NewDecoder
have (billy.File)
...

Fixed in commit 0c4fa2f: verify-pack now passes the selected hash implementation to idxfile.NewDecoder (hash.New(ch)), which resolves the v6 API compilation error. I also verified with make build, go test ./..., and make validate-lint.