pyproject: add build-system stanza for Guix packaging HEAD main

Without a [build-system] table Guix's pyproject-build-system has no
backend to invoke.  Declare setuptools so the package builds cleanly.

1 files changed, 4 insertions, 0 deletions

diff --git a/pyproject.toml b/pyproject.toml
index 6a8f9a4..e94e642 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -16,3 +16,7 @@ markers = [
     "gn_auth: Tests exercising the gn-auth service",
     "auth_flow: Tests requiring valid user credentials (set GN_TEST_EMAIL and GN_TEST_PASSWORD)",
 ]
+
+[build-system]
+requires = ["setuptools"]
+build-backend = "setuptools.backends.legacy:build"