This commit updates `github.com/libgit2/git2go` to `v31.6.1` (with
`libgit2` `1.1.1`), and changes the container image build process so
that it makes use of `ghcr.io/hiddeco/golang-with-libgit2`.
This image provides a pre-build dynamic `libgit2` dependency linked
against OpenSSL and LibSSH2 (without gcrypt), and a set of cross-compile
build tools (see
[rationale](https://github.com/hiddeco/golang-with-libgit2#rationale) and
[usage](https://github.co/hiddeco/golang-with-libgit2#usage) for more
detailed information).
The linked set of dependency should solve most known issues around
unsupport private key types, but does not resolve the issues with ECDSA*
and ED25519 hostkeys yet. Solving this requires a newer version of
`libgit2` (`>=1.2.0`), which currently does not seem to work properly
with `git2go/v32`.
Some small changes have been made to the `libgit2` package to address
(future) deprecations.
Signed-off-by: Hidde Beydals <hello@hidde.co>