sync subcommand with --pull does not support negative refspecs

[ryan-ph]

Description of the bug

Git v2.29.0 supports negative refspecs to allow filtering which refspecs to ignore.

It seems like git branchless sync --pull does not currently respect this and will cause panics if a negative refspec is specified in the git config.

Example git config specifying a negative refspec for any branches with an underscore prefix

[remote "origin"]
    fetch = ^refs/heads/_*

Expected behavior

When running git branchless sync --pull, I expect all refs to be fetched from the remote following all git refspec rules (i.e. all refs which match postive refspecs and do not match any negative refspecs), and all local refs to be updated.

Actual behavior

A panic:

$ git sync --pull
branchless: running command: git fetch --all
branchless: processing 1 update: remote branch origin/master
From github.com:**********
   1cbda20c5530..7aebefa5462d  master        -> origin/master
branchless: processing 1 update: remote branch origin/fix-inventory
 * [new branch]                fix-inventory -> origin/fix-inventory
The application panicked (crashed).
Message:  A fatal error occurred:
   0: could not find upstream branch for branch with name 'master': '^refs/heads/_*' is not a valid refspec.; class=Invalid (3)
   1: '^refs/heads/_*' is not a valid refspec.; class=Invalid (3)

Version of rustc

No response

Automated bug report

No response

Version of git-branchless

git-branchless-opts 0.10.0

Version of git

git version 2.44.0

[ryan-ph]

Seems like this is an upstream issue: libgit2/libgit2#6741