Fix function grouping skipped for lowercase 'as' in CREATE TABLE AS SELECT

[Osamaali313]

• ran the tests (pytest)
• all style issues addressed (ruff)
• your changes are covered by tests
• your changes are documented, if needed

In group_functions (sqlparse/engine/grouping.py), the guard that suppresses function grouping for CREATE TABLE name (...) checks three tokens, but only two are case-insensitive:

if tmp_token.value.upper() == 'CREATE':
    has_create = True
if tmp_token.value.upper() == 'TABLE':
    has_table = True
if tmp_token.value == 'AS':        # case-sensitive
    has_as = True

Since SQL keywords are case-insensitive, a lowercase as in a CREATE TABLE ... AS SELECT (CTAS) statement leaves has_as False, so the guard fires and grouping returns early, skipping all function grouping for the statement.

import sqlparse
from sqlparse import sql

p = sqlparse.parse("CREATE TABLE foo as SELECT count(x) FROM bar")[0]
# count(x) is left as a bare Name + Parenthesis instead of a sql.Function

With uppercase AS the same statement groups count(x) as a Function; only the keyword casing changes the parse tree. The existing test_grouping_alias_ctas covers the uppercase form.

The fix compares as case-insensitively like its sibling checks, and I added a lowercase regression test. The original guard behavior is preserved: create table foo (a int, b int) (no AS) still does not group foo (...) as a function in either case.

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