message: Make ExecuteContext const in PjRtExecutable ExecuteOptions.
diff: @@ -695,7 +695,7 @@ struct ExecuteOptions {
  int32 launch_id = 0;
  // If non-null, an opaque context passed to an execution that may be used to
  // supply additional arguments to a derived class of PjRtExecutable.
  - ExecuteContext* context = nullptr;
  + const ExecuteContext* context = nullptr;
  };
  // Represents a compiled computation that can be executed given handles to
  