chore: update webchat to 4.15.3 (#9344)

Author: OEvgeny

Composer/packages/client/package.json

@@ -55,8 +55,8 @@
     "ansi_up": "5.0.0",
     "axios": "^0.21.1",
     "babel-plugin-extract-format-message": "^6.2.3",
-    "botframework-webchat": "4.15.1",
-    "botframework-webchat-core": "4.15.1",
+    "botframework-webchat": "4.15.3",
+    "botframework-webchat-core": "4.15.3",
     "format-message": "6.2.4",
     "format-message-generate-id": "^6.2.3",
     "immer": "^9.0.6",