setup: pass named argument to setup_zstd

The next release from upstream adds another named argument to this
function. Specify arguments by name so there is no ambiguity about
which argument is being passed.

setup.py

@@ -615,7 +615,7 b' extmodules = ['
 
 sys.path.insert(0, 'contrib/python-zstandard')
 import setup_zstd
-extmodules.append(setup_zstd.get_c_extension('mercurial.zstd'))
+extmodules.append(setup_zstd.get_c_extension(name='mercurial.zstd'))
 
 try:
     from distutils import cygwinccompiler