black: rename pyproject.toml to black.toml
Black won't read this automatically (you'll have to specify --config),
but having a pyproject.toml *at all* puts pip in PEP 517/518 mode
which breaks us for obscure reasons I don't understand. Rather than
waste a ton of time fighting with pip, let's just do this.
Differential Revision: https://phab.mercurial-scm.org/D7087
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}