Check getint, getboolean behavior in config file

We were probably silently catching a lot of ValueError and TypeError in these excepts so far, especially for getboolean and getint. Not sure if we should also handle that in here? Haven't tested with offending values yet :)

Originally posted by @nejch in https://github.com/python-gitlab/python-gitlab/pull/2212#discussion_r936706808

Since we haven't heard any complaints I'm thinking this might not be an issue at all, and people will just get the error thrown if they misconfigure their config files.