update openff-workshop version to 2026-01-15

Author: jimboid

workshop.json

@@ -65,6 +65,9 @@
     },
     "coarse-graining-workshop": {
       "latest": "2026-01-12"
+    },
+    "openff-workshop": {
+      "latest": "2026-01-15"
     }
   }
 }