`checker`: Remove `{}` in `test_err()`

The test_err() function was using a lingering artifact ({}) from the use of xargs in other tests. This failed the test.

This commit removes the lingering artifact. The test now passes.

Signed-off-by: Razvan Deaconescu razvan.deaconescu@upb.ro

approved this merge request

mentioned in commit 27211c4e

merged