Use UTF-8 when processing specification tests.

* tests/spec/oil.scm: Set the encoding on the input and output ports
to UTF-8.

tests/spec/oil.scm

@@ -90,6 +90,11 @@
                     (format #t "Removing tests from ~a:~%" file)
                     (with-atomic-file-replacement file
                       (lambda (in out)
+                        ;; The Oil tests are encoded as UTF-8, so we
+                        ;; set the encoding on the two ports to ensure
+                        ;; that Guile preserves non-ASCII characters.
+                        (set-port-encoding! in "UTF-8")
+                        (set-port-encoding! out "UTF-8")
                         (let loop ((line (read-line in 'concat))
                                    (transformers #t))
                           (cond