Fix typos in mmap() error messages (GH-6173)

(cherry picked from commit 9308dea3e1fd565d50a76a667e4e8ef0568b7053)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index 95d42d6..9afb79f 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -1067,7 +1067,7 @@
         return NULL;
     if (map_size < 0) {
         PyErr_SetString(PyExc_OverflowError,
-                        "memory mapped length must be postiive");
+                        "memory mapped length must be positive");
         return NULL;
     }
     if (offset < 0) {
@@ -1253,7 +1253,7 @@
 
     if (map_size < 0) {
         PyErr_SetString(PyExc_OverflowError,
-                        "memory mapped length must be postiive");
+                        "memory mapped length must be positive");
         return NULL;
     }
     if (offset < 0) {