bug: literal in arguments should not be casted into lowercase

[sundy-li]

literal in arguments should not be casted into lowercase

🐳 :) select siphash('y'), siphash('Y');
┌───────────────────────────────────────────┐
│     siphash('y')    │     siphash('y')    │
│        UInt64       │        UInt64       │
├─────────────────────┼─────────────────────┤
│ 5356863688430645057 │ 9746634682266333199 │
└───────────────────────────────────────────┘
1 row read in 0.007 sec. Processed 1 row, 1B (135.49 row/s, 135B/s)

Originally posted by @sundy-li in https://github.com/datafuselabs/databend/issues/14775#issuecomment-2008525527

[wubx]

It feels right.

[sundy-li]

@dosubot how to fix this issue ?