bpo-32030: Fix config_get_program_name() on macOS (#4669)

diff --git a/Modules/main.c b/Modules/main.c
index 6c1cf0d..6c6c801 100644
--- a/Modules/main.c
+++ b/Modules/main.c
@@ -894,7 +894,7 @@
             return SET_DECODE_ERROR("PYTHONEXECUTABLE environment "
                                     "variable", len);
         }
-        pymain->config.program_name = buffer;
+        config->program_name = program_name;
     }
 #ifdef WITH_NEXT_FRAMEWORK
     else {
@@ -909,7 +909,7 @@
                 return SET_DECODE_ERROR("__PYVENV_LAUNCHER__ environment "
                                         "variable", len);
             }
-            pymain->config.program_name = program_name;
+            config->program_name = program_name;
         }
     }
 #endif   /* WITH_NEXT_FRAMEWORK */