Fix typos in comments, docs and test names (#15018)

* Fix typos in comments, docs and test names

* Update test_pyparse.py

account for change in string length

* Apply suggestion: splitable -> splittable

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Apply suggestion: splitable -> splittable

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Apply suggestion: Dealloccte -> Deallocate

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Update posixmodule checksum.

* Reverse idlelib changes.
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 0995b1e..36a2653 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -1420,7 +1420,7 @@
         # Initialize with invalid argument
         self.assertRaises(TypeError, lambda: self._factory(object()))
 
-    def test_all_eMM_attribues_exist(self):
+    def test_all_eMM_attributes_exist(self):
         # Issue 12537
         eMM = email.message_from_string(_sample_message)
         msg = self._factory(_sample_message)