Log Message:
libgit2: update to 1.6.2.

Bug fixes

    remote: always populate old id in update tips by @ethomson in #6506
    The update tips callback would not always be properly provided with an empty \ 
(0000000...) OID for new refs.

    Revert #6503 by @ethomson in #6511
    The certificate callback added port information for callbacks in #6503, but \ 
the format was ambiguous with IPv6 addresses. Revert this change temporarily.

    Add git_odb_backend_loose back by @ethomson in #6512
    During SHA256 refactoring, the git_odb_backend_loose API was accidentally \ 
removed. Add it back.

    meta: configure pkg-config .pc correctly by @ethomson in #6514
    During SHA256 refactoring, the pkg-config .pc file was erroneously renamed \ 
to git2 instead of libgit2. Repair this.