Exclude LinLibertine_I.otf for en language coverage

LinLibertine_I is "Linux Libertine Initials" not the italic version of Linux Libertine.
It is LinLibertine_RI.otf.

tests/tests.yml

@@ -8,7 +8,9 @@
     - linux-libertine-biolinum-fonts
     path_prefix: /usr/share/fonts/linux-libertine
     coverage:
-    - en
+      en:
+        exclude:
+          - LinLibertine_I.otf
     families:
     - lang: en
       alias: serif