bpo-36969: Make PDB args command display positional only arguments (GH-13459)

diff --git a/Lib/pdb.py b/Lib/pdb.py
index 0e7609e..13068ce 100755
--- a/Lib/pdb.py
+++ b/Lib/pdb.py
@@ -1132,7 +1132,7 @@
         """
         co = self.curframe.f_code
         dict = self.curframe_locals
-        n = co.co_argcount + co.co_kwonlyargcount
+        n = co.co_argcount + co.co_posonlyargcount + co.co_kwonlyargcount
         if co.co_flags & inspect.CO_VARARGS: n = n+1
         if co.co_flags & inspect.CO_VARKEYWORDS: n = n+1
         for i in range(n):