bpo-35133: Fix mistakes when concatenate string literals on different lines. (GH-10284)

Two kind of mistakes:

1. Missed space. After concatenating there is no space between words.

2. Missed comma. Causes unintentional concatenating in a list of strings.

Python/import.c

@@ -839,7 +839,7 @@ remove_module(PyObject *name)
         if (!PyMapping_HasKey(modules, name)) {
             return;
         }
-        Py_FatalError("import:  deleting existing key in"
+        Py_FatalError("import:  deleting existing key in "
                       "sys.modules failed");
     }
 }