Fix test-font leak issue

See also https://github.com/harfbuzz/harfbuzz/pull/1169
diff --git a/test/api/test-font.c b/test/api/test-font.c
index 527dfcd..4a2393e 100644
--- a/test/api/test-font.c
+++ b/test/api/test-font.c
@@ -361,6 +361,7 @@
 
 
   hb_font_destroy (font3);
+  hb_font_destroy (font2);
 }