Fix typos mostly in comments, docs and test names (GH-15209)

Python/ast.c

@@ -5356,7 +5356,7 @@ typedef struct {
        doubling the number allocated each time. Note that the f-string
        f'{0}a{1}' contains 3 expr_ty's: 2 FormattedValue's, and one
        Constant for the literal 'a'. So you add expr_ty's about twice as
-       fast as you add exressions in an f-string. */
+       fast as you add expressions in an f-string. */
 
     Py_ssize_t allocated;  /* Number we've allocated. */
     Py_ssize_t size;       /* Number we've used. */