bpo-37116: Use PEP 570 syntax for positional-only parameters. (GH-13700)

diff --git a/Lib/idlelib/debugger_r.py b/Lib/idlelib/debugger_r.py
index 0e6dcfb..9dcfc56 100644
--- a/Lib/idlelib/debugger_r.py
+++ b/Lib/idlelib/debugger_r.py
@@ -299,7 +299,7 @@
         self.conn = conn
         self.shell = shell
 
-    def call(self, methodname, *args, **kwargs):
+    def call(self, methodname, /, *args, **kwargs):
         ##print("*** IdbProxy.call %s %s %s" % (methodname, args, kwargs))
         value = self.conn.remotecall(self.oid, methodname, args, kwargs)
         ##print("*** IdbProxy.call %s returns %r" % (methodname, value))