py-dulwich: updated to 0.20.40

0.20.40
* Fix wheel uploading.

0.20.38
* Disable paramiko tests if paramiko is not available.
* Set flag to re-enable paramiko server side on gentoo for running paramiko
  tests.
* Increase tolerance when comparing time stamps; fixes some
  spurious test failures on slow CI systems.
* Revert removal of caching of full HTTP response. This breaks
  access to some HTTP servers.

0.20.37
* Avoid making an extra copy when fetching pack files.
* Add ``porcelain.remote_remove``.

0.20.36
* Add ``walk_untracked`` argument to ``porcelain.status``.
* Add tests for paramiko SSH Vendor.

(adam)