Remove initial newline from automatically generated span tests

This change was accidentally introduced while removing license headers.

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

@@ -13,7 +13,7 @@
 TEST_DIR = os.path.abspath(
     os.path.join(os.path.dirname(__file__), '../test/ui/derives/'))
 
-TEMPLATE = """
+TEMPLATE = """\
 // This file was auto-generated using 'src/etc/generate-deriving-span-tests.py'
 
 {error_deriving}