[la.container] fix warning

dune/xt/common/disable_warnings.hh

@@ -18,6 +18,7 @@
 #  pragma GCC diagnostic ignored "-Wall"
 #  pragma GCC diagnostic ignored "-Wcovered-switch-default"
 #  pragma clang diagnostic ignored "-Wdelete-non-virtual-dtor"
+#  pragma GCC diagnostic ignored "-Wdeprecated-copy"
 #  pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 #  pragma GCC diagnostic ignored "-Wdeprecated-register"
 #  pragma GCC diagnostic ignored "-Wdisabled-macro-expansion"
@@ -50,6 +51,7 @@
 #  pragma GCC diagnostic push
 #  pragma GCC diagnostic ignored "-Wall"
 #  pragma GCC diagnostic ignored "-Wattributes"
+#  pragma GCC diagnostic ignored "-Wdeprecated-copy"
 #  pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 #  pragma GCC diagnostic ignored "-Wextra"
 #  pragma GCC diagnostic ignored "-Wfloat-equal"

dune/xt/la/container/eigen/dense.hh

@@ -185,6 +185,8 @@ public:
 
   using BaseType::operator=;
 
+  ThisType& operator=(const ThisType& other) = default;
+
   ThisType& operator=(const BackendType& other)
   {
     backend_ = std::make_shared<BackendType>(other);