Fix invalid path in generate-deriving-span-tests.py.

This script broke after rust-lang#53196 after the tests were moved.

Author: frewsxcv

src/etc/generate-deriving-span-tests.py

@@ -21,7 +21,7 @@
 import sys, os, datetime, stat, re
 
 TEST_DIR = os.path.abspath(
-    os.path.join(os.path.dirname(__file__), '../test/compile-fail'))
+    os.path.join(os.path.dirname(__file__), '../test/ui/derives/'))
 
 YEAR = datetime.datetime.now().year