Validation failure (and fix)

Please provide the following

• Machine and OS: Linux Ubuntu 22.04
• binary_c: branch: commit:4fa692b95
• binary_c-python: branch: commit:9b8d2949

The population option "symlink_latest_gridcode" is validated as a string in population_options_defaults.py, but set to True, which causes a validation failure when I try to set this (later) to False.

Changing its type to boolean_int_validation seems to fix things, but please check this is right before I break something else :)