Avoid const char to char now invalid pointer convert

Summary:
This change allows the code to compile using the C23 standard.

Ref T2213

Test Plan:

• Build the library
• load ./fbsql.so ; sql connect 127.0.0.1 ; sql "SELECT 1+1"

Maniphest Tasks: T2213

Differential Revision: https://devcentral.nasqueron.org/D3910