Setting GIT_SSH_COMMAND environment variable breaks conversion

Some update has broken my hg workflow and after some debugging I think it might be hg-git.

This does not work anymore:

GIT_SSH_COMMAND='ssh -i ~/.ssh/id_rsa.mykey' hg clone git@github.com:takelwerk/rake-meta.git

But this works:

GIT_GIT_SSH_COMMAND='ssh -i ~/.ssh/id_rsa.mykey' hg clone git@github.com:takelwerk/rake-meta.git

I've guessed the second line from the error message:

$ GIT_SSH_COMMAND='ssh -i ~/.ssh/id_rsa.mykey' hg clone git@github.com:takelwerk/rake-meta.git
** unknown exception encountered, please report by visiting
** https://mercurial-scm.org/wiki/BugTracker
** Python 3.9.2 (default, Feb 28 2021, 17:03:44) [GCC 10.2.1 20210110]
** Mercurial Distributed SCM (version 5.6.1)
** Extensions loaded: hggit
Traceback (most recent call last):
  File "/usr/bin/hg", line 43, in <module>
    dispatch.run()
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 113, in run
    status = dispatch(req)
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 303, in dispatch
    ret = _runcatch(req) or 0
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 479, in _runcatch
    return _callcatch(ui, _runcatchfunc)
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 488, in _callcatch
    return scmutil.callcatch(ui, func)
  File "/usr/lib/python3/dist-packages/mercurial/scmutil.py", line 153, in callcatch
    return func()
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 469, in _runcatchfunc
    return _dispatch(req)
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 1232, in _dispatch
    return runcommand(
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 917, in runcommand
    ret = _runcommand(ui, options, cmd, d)
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 1244, in _runcommand
    return cmdfunc()
  File "/usr/lib/python3/dist-packages/mercurial/dispatch.py", line 1230, in <lambda>
    d = lambda: util.checksignature(func)(ui, *args, **strcmdopt)
  File "/usr/lib/python3/dist-packages/mercurial/util.py", line 1867, in check
    return func(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/mercurial/commands.py", line 1895, in clone
    r = hg.clone(
  File "/var/lib/mercurial/hgext/hg-git/hggit/schemes.py", line 92, in clone
    srcpeer, destpeer = orig(*args, **opts)
  File "/usr/lib/python3/dist-packages/mercurial/hg.py", line 928, in clone
    exchange.pull(
  File "/var/lib/mercurial/hgext/hg-git/hggit/util.py", line 74, in inner
    return f(*args, **kwargs)
  File "/var/lib/mercurial/hgext/hg-git/hggit/gitrepo.py", line 197, in exchangepull
    pullop.cgresult = repo.githandler.fetch(remote, heads)
  File "/var/lib/mercurial/hgext/hg-git/hggit/git_handler.py", line 323, in fetch
    result = self.fetch_pack(remote.path, heads)
  File "/var/lib/mercurial/hgext/hg-git/hggit/git_handler.py", line 1358, in fetch_pack
    ret = self._call_client(remote, 'fetch_pack', determine_wants,
  File "/var/lib/mercurial/hgext/hg-git/hggit/git_handler.py", line 1395, in _call_client
    return func(path, *args, **kwargs)
  File "/usr/local/lib/python3.9/dist-packages/dulwich/client.py", line 1019, in fetch_pack
    proto, can_read, stderr = self._connect(b"upload-pack", path)
  File "/usr/local/lib/python3.9/dist-packages/dulwich/client.py", line 1687, in _connect
    con = self.ssh_vendor.run_command(
TypeError: run_command() got an unexpected keyword argument 'ssh_command'

It is correct that dulwich fails because the name of the environment variable is GIT_SSH_COMMAND and not SSH_COMMAND. So I guess the problem is one step up which is hg-git.

I am using hggit external 0.11.0dev (dulwich 0.20.26) on Debian 11 with Python 3.9.2.