chore: adds xunit to cspell configuration

Signed-off-by: Vincent Biret <vibiret@microsoft.com>

Author: baywet

.vscode/settings.json

@@ -6,6 +6,7 @@
     },
     "cSpell.words": [
         "csdl",
-        "Hidi"
+        "Hidi",
+        "Xunit"
     ]
 }