tests: style: Fix insufficient number of lines read.

* tests/style.scm ("url-fetch->git-fetch, preserved field"):

The 9th line of origin, where the patches field is located,
was never read. (broken test since a1b0fde434)

tests/style.scm

@@ -655,7 +655,7 @@
                          "https://github.com/foo/bar"))
                       (load file)
                       (and=> (read-package-field
-                              (@ (my-packages-1) my-coreutils-1) 'source 8)
+                              (@ (my-packages-1) my-coreutils-1) 'source 9)
                              (cut string-contains <> "patches")))))))
     "1"))