thai_strftime: Output for unsupported directive looks different on Alpine

[bact]

Describe the bug

On a system that use musl (like Alpine), thai_strftime() will handle unsupported directive differently from glibc.

Although the behavior is undefined in C89 standard, the user may expect a consistent behavior across platforms.

To Reproduce

from datetime import datetime, timezone
from pythainlp.util import thai_strftime

date = datetime(1976, 10, 6, 1, 40, tzinfo=timezone.utc)
thai_strftime(date, "%Q")  # unsupported directive

Expected behavior

thai_strftime(date, "%Q") should return "Q" independently from the underlying platform.