go-git: Improper single-quote escaping in go-git SSH transport

### Impact `go-git`'s SSH transport constructs the remote exec command by wrapping the repository path in single quotes without escaping single quotes embedded inside the path. This diverges from canonical Git, which shell-quotes the path through `sq_quote_buf` so that an embedded `'` becomes the `'\''` close-escape-reopen sequence and the whole path round-trips as a single quoted argument. A repository path containing a single quote can therefore break out of the quoted region in the exec command and be appended as additional shell tokens. On SSH servers that evaluate the exec command through a shell (for example a user account whose login shell is `/bin/sh` or `/bin/bash`, or a `ForceCommand` wrapper that re-evaluates `$SSH_ORIGINAL_COMMAND`), those additional tokens execute in that account's command-execution context. SSH servers that tokenize the exec command without shell evaluation, including the canonical `git-shell` setup, are not affected. The vulnerable behaviour is on the SSH server side, not in `go-git`: the same bytes can be produced by any SSH client. The change in `go-git` is defense-in-depth that restores parity with canonical Git's wire format and prevents `go-git` from being a vehicle for reaching shell-evaluating servers through attacker-influenced repository paths. ### Patches Users should upgrade to a patched version in order to mitigate this issue. The fix ports `sq_quote_buf` from canonical Git into `go-git`'s SSH transport so that the wire output is byte-identical to what `git` itself would send for the same input. Versions prior to `v5` are likely to be affected, users are recommended to upgrade to a supported go-git version. ### Credit Thanks to @N0zoM1z0 for reporting this to the `go-git` project. :bow: