mkvenv: mark command as required

This is only available in Python 3.7+.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20230511035435.734312-26-jsnow@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/python/scripts/mkvenv.py b/python/scripts/mkvenv.py
index 5586199..8c036c0 100644
--- a/python/scripts/mkvenv.py
+++ b/python/scripts/mkvenv.py
@@ -854,6 +854,7 @@ def main() -> int:
     subparsers = parser.add_subparsers(
         title="Commands",
         dest="command",
+        required=True,
         metavar="command",
         help="Description",
     )