Add version_info checks again, pending migration to pyproject

pyproject.toml

@@ -2,9 +2,6 @@
 requires = ["setuptools", "wheel"]
 build-backend = "setuptools.build_meta"
 
-[project]
-requires-python = ">=3.9"
-
 [tool.pytest.ini_options]
 pythonpath = [
   ".",

setup_rucio.py

@@ -19,6 +19,10 @@
 
 from setuptools import find_packages, setup
 
+if sys.version_info < (3, 9):  # noqa: UP036 (pending https://github.com/rucio/rucio/issues/6971)
+    print('ERROR: Rucio Server requires at least Python 3.9 to run.')
+    sys.exit(1)
+
 try:
     from setuputil import get_rucio_version, match_define_requirements, server_requirements_table
 except ImportError:

setup_rucio_client.py

@@ -18,6 +18,10 @@
 
 from setuptools import setup
 
+if sys.version_info < (3, 9):  # noqa: UP036 (pending https://github.com/rucio/rucio/issues/6971)
+    print('ERROR: Rucio Client requires at least Python 3.9 to run.')
+    sys.exit(1)
+
 try:
     from setuputil import clients_requirements_table, get_rucio_version, match_define_requirements
 except ImportError:

setup_webui.py

@@ -17,6 +17,10 @@
 
 from setuptools import setup
 
+if sys.version_info < (3, 9):  # noqa: UP036 (pending https://github.com/rucio/rucio/issues/6971)
+    print('ERROR: Rucio Server requires at least Python 3.9 to run.')
+    sys.exit(1)
+
 try:
     from setuputil import get_rucio_version
 except ImportError: