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>

checker/checker.sh

@@ -10,7 +10,7 @@ test_err()
     local temp_output=''
     temp_output="$(mktemp)"
 
-    timeout "$TIMEOUT_DURATION" bash -c "$EXECUTABLE {} > $temp_output 2>&1"
+    timeout "$TIMEOUT_DURATION" bash -c "$EXECUTABLE > $temp_output 2>&1"
 
     diff -Zq "$temp_output" "./references/ref1" > /dev/null 2>&1
     return $?