PLT-6503 Updated error when invalid image is uploaded as profile picture (#6508)

i18n/en.json

@@ -2737,7 +2737,7 @@
   },
   {
     "id": "api.user.upload_profile_user.decode_config.app_error",
-    "translation": "Could not decode profile image config."
+    "translation": "Could not save profile image. File does not appear to be a valid image."
   },
   {
     "id": "api.user.upload_profile_user.encode.app_error",