Convert warnings on CI to errors

Currently warnings on CI can get lost in the logs. It may be helpful to have some (or all) jobs convert warnings to errors so that we can better catch and fix issues that crop up.

Inspect the repository's CI configuration and identify which jobs currently allow warnings to pass unnoticed. Determine whether some or all jobs should treat warnings as errors, then verify that the selected jobs fail when warnings occur and continue to pass without them.

Written by the indexing model from the issue text.