adding towncrier wrapper script so 'tox -e docs' works natively on windows (#7266)

* enable tox -e docs natively on windows using a wrapper

* rename the towncrier script; run the towncrier command in a safer manner

* use subprocess.call; call exit() around main on towncrier wrapper

* change to sys.exit() instead of builtin exit()

scripts/towncrier-draft-to-file.py

@@ -0,0 +1,15 @@
+import sys
+from subprocess import call
+
+
+def main():
+    """
+    Platform agnostic wrapper script for towncrier.
+    Fixes the issue (#7251) where windows users are unable to natively run tox -e docs to build pytest docs.
+    """
+    with open("doc/en/_changelog_towncrier_draft.rst", "w") as draft_file:
+        return call(("towncrier", "--draft"), stdout=draft_file)
+
+
+if __name__ == "__main__":
+    sys.exit(main())

tox.ini

@@ -80,9 +80,8 @@ usedevelop = True
 deps =
     -r{toxinidir}/doc/en/requirements.txt
     towncrier
-whitelist_externals = sh
 commands =
-    sh -c 'towncrier --draft > doc/en/_changelog_towncrier_draft.rst'
+    python scripts/towncrier-draft-to-file.py
     # the '-t changelog_towncrier_draft' tags makes sphinx include the draft
     # changelog in the docs; this does not happen on ReadTheDocs because it uses
     # the standard sphinx command so the 'changelog_towncrier_draft' is never set there