test.testers: fix getAllOutputNames not found

pkgs/build-support/testers/expect-failure.sh

···
 
 # -----------------------------------------
 # Write the build log to the default output
+#
+# # from stdenv setup.sh
+getAllOutputNames() {
+    if [ -n "$__structuredAttrs" ]; then
+        echo "${!outputs[*]}"
+    else
+        echo "$outputs"
+    fi
+}
 
 outs=( $(getAllOutputNames) )
 defOut=${outs[0]}