Restore py3.9 backwards compatibility

Author: fqqb

setup.py

@@ -36,7 +36,7 @@
         "Operating System :: OS Independent",
     ],
     platforms="Posix; MacOS X; Windows",
-    install_requires=["argcomplete", "python-dateutil", "yamcs-client>=1.12.0"],
+    install_requires=["argcomplete", "python-dateutil", "yamcs-client>=1.12.1"],
     extras_require={"kerberos": ["yamcs-client-kerberos>=1.3.0"]},
     include_package_data=True,
     zip_safe=False,

src/yamcs/cli/__main__.py

@@ -95,7 +95,11 @@ def main():
     TablesCommand(subparsers)
 
     # Discover subcommand plugins
-    for entry in entry_points(group="yamcs.cli.subcommands"):
+    try:
+        eps = entry_points(group="yamcs.cli.subcommands")
+    except TypeError:  # < Python 3.10
+        eps = entry_points().get("yamcs.cli.subcommands", [])
+    for entry in eps:
         subcommand_cls = entry.load()
         subcommand_cls(subparsers)