rav1e: build fails on arm, due to git_allocator missing members; git2 crate [used by rav1e] may need to be updated

[lukaso (Lukas Oberhuber)]

First reported on ​https://trac.macports.org/ticket/68026, via @macsguy:

This may require updating the version of the git2 crate [used by rav1e], now that libgit2 has been updated to 1.7.1:

libgit2/src/util/array.h:59:19: error: no member named 'greallocarray' in 'git_allocator'
        if ((new_array = git__reallocarray(a->ptr, new_size, item_size)) == NULL)
                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

libgit2/src/libgit2/annotated_commit.c:34:21: error: no member named 'gcalloc' in 'git_allocator'
        annotated_commit = git__calloc(1, sizeof(git_annotated_commit));
                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

libgit2/src/libgit2/annotated_commit.c:48:34: error: no member named 'gstrdup' in 'git_allocator'
        annotated_commit->description = git__strdup(description);
                                        ^~~~~~~~~~~~~~~~~~~~~~~~

I gave a shot at trying to update the crates, but got errors after updating the crate list:

:info:extract error: failed to select a version for the requirement `git2 = "^0.15"`
:info:extract candidate versions found which didn't match: 0.18.0
:info:extract location searched: directory source `/Users/lukasoberhuber/macports-gimp3-arm64/var/macports/build/_Users_lukasoberhuber_project_ports_multimedia_rav1e/rav1e/work/.home/.cargo/macports` (which is replacing registry `crates-io`)
:info:extract required by package `built v0.5.2`
:info:extract     ... which satisfies dependency `built = "^0.5.2"` of package `rav1e v0.6.6 (/Users/lukasoberhuber/macports-gimp3-arm64/var/macports/build/_Users_lukasoberhuber_project_ports_multimedia_rav1e/rav1e/work/rav1e-0.6.6)`
:info:extract perhaps a crate was updated and forgotten to be re-vendored?
:info:extract As a reminder, you're using offline mode (--offline) which can sometimes cause surprising resolution failures, if this error is too confusing you may wish to retry without the offline flag.
:info:extract Command failed: /Users/lukasoberhuber/macports-gimp3-arm64/bin/cargo --offline update
:info:extract Exit code: 101

[lukaso (Lukas Oberhuber)]

Has multiple builds in it, so just focus on last one (they appear to be all the same, which might mean that macports tried to run it multiple times)