Add tests for older cfgs

[forsyth2]

Request criteria

• I searched the zppy GitHub Discussions to find a similar question and didn't find it.
• I searched the zppy documentation.
• This issue does not match the other templates (i.e., it is not a bug report, documentation request, feature request, or a question.)

Issue description

Currently, zppy's test cfg files get updated as parameters change. We need some way to test that older cfgs still work. This would cover cases like:

• Is that new parameter in main required, or can it be safely ignored?
• Does that deprecated parameter in this old cfg give a warning/error?