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

contrib/examples/fix.hgrc

@@ -11,5 +11,5 b' rustfmt:pattern = set:**.rs'
 # git+https://github.com/python/black/@d9e71a75ccfefa3d9156a64c03313a0d4ad981e5
 # to have the dependencies for grey.
 #
-# black:command = python3.7 contrib/grey.py --quiet --skip-string-normalization -
+# black:command = python3.7 contrib/grey.py --quiet --config=black.toml --skip-string-normalization -
 # black:pattern = set:**.py - hgext/fsmonitor/pywatchman/** - mercurial/thirdparty/** - "contrib/python-zstandard/**"

tests/test-check-code.t

@@ -64,10 +64,10 b' Prevent adding new files in the root dir'
   COPYING
   Makefile
   README.rst
+  black.toml
   hg
   hgeditor
   hgweb.cgi
-  pyproject.toml
   setup.py
 
 Prevent adding modules which could be shadowed by ancient .so/.dylib.