Disagreement with CPython for str.islower/isupper/swapcase

## Python Documentation or reference to CPython source code

tested on current main: 1a9b10ece50ebdbdd3820dafa8f6a630d87be9c0

There are many examples and I picked one.

```py
# the following is True in CPython and False in RustPython
print(
    "\u0295".islower() == True,
    "\u1c89".isupper() == False,
    "Σίσυφος".swapcase() == "σΊΣΥΦΟΣ",
)
```
