Remove warning by changing sprintf to snprintf in geos_ts_c.cpp

[Maxxen]

On Apple clang version 14.0.0 (clang-1400.0.29.202) compiling geos_ts_c.cpp with -Werror,-Wdeprecated-declarations fails with:

'sprintf' is deprecated: This function is provided for compatibility reasons only. Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead.

This is the only use of sprintf I could find and since the buffer is already constant sized it makes sense to use snprintf instead to remove the warning.

[dbaston]

Thanks!