Failed Evergreen non-unittest tasks have the "Unit Tests" link on them, some of which are tarballs that are in the GBs. E.g. this one is 1.8GB.
The unzipped file showed binaries and debug symbols for mongo/d/s that "gather failed unittests" is picking.
We should have the function not run for non-unittest tasks. This requires a change in evergreen.yaml.