Fix typo 'unpickable' -> 'unpickleable' (#13344)

Normalize other occurrences of '~picklable' to '~pickleable'.

Note, there is no clear winner in the Python docs regarding usage of '~picklable' vs '~pickleable', so we pick the more greppable version.

tests/test_versioning.py

@@ -49,7 +49,7 @@ def test_add_uids():
     assert len(original_uids) == 3
 
 
-def test_picklablility():
+def test_pickleablility():
     # we have to modify the doctree so we can pickle it
     copy = original.copy()
     copy.reporter = None