Use different exit codes for data threshold warnings

[mikewilli]

It seems like there is some collision happening with the toml decoder (https://github.com/mozilla/metric-hub/actions/runs/20862042166/job/59943912098?pr=1304), so let's try some different exit codes for these warnings.

Will also require metric-hub CI updates to use the new codes.

┆Issue is synchronized with this Jira Task