libgrapheme: is currently broken in linux

It's fixed in master, but there's not release yet. In [1] there
was a discussion to deliberately let the windows tests fail. As the
current PR seems to be ignored until the pipeline is green, I'm trying
to fix the pipeline nonetheless.

[1] #2136

Author: Gottox

ci_config.json

@@ -16,7 +16,8 @@
     "mocklibc",
     "termbox",
     "m4",
-    "tinyply"
+    "tinyply",
+    "libgrapheme"
   ],
   "broken_darwin": [
     "arduinocore-avr",