Fix missing pgi.foreign package in tarballs

Tarballs built using ./setup.py sdist and uploaded to PyPI
don't include pgi.foreign package making pgi unusable.

setup.py

@@ -239,6 +239,7 @@ def run(self):
          'pgi.cffilib.gir',
          'pgi.cffilib.glib',
          'pgi.cffilib.gobject',
+         'pgi.foreign',
          'pgi.overrides',
          'pgi.repository',
          'pgi.codegen',