docs: Add "special" to the Alex allowlist (#48021)

It's a common word we use in our docs, e.g.:


e35710f71f/docs/advanced-features/open-telemetry.md (L105)

.alexrc

@@ -18,6 +18,7 @@
     "host-hostess",
     "invalid",
     "remains",
+    "special",
     "white"
   ]
 }