Fix build warnings in 3.5.2 from GCC/12

[pdbj]

Describe the bug A handful of compiler warnings from GCC/12 (with web server disabled)

Patch attached.

Environment (please complete the following information):

• Operating System: Linux
• Compiler: GCC/12.1.1
• HELICS version: 3.5.2

helics-3.5.2-gcc-12.patch