try to fix build error on gh actions

Author: pachadotdev

inst/include/cpp11/matrix.hpp

@@ -190,11 +190,13 @@ class matrix : public matrix_slices<S> {
 
   operator SEXP() const { return SEXP(vector_); }
 
-  attribute_proxy<V> attr(const char* name) { return vector_.attr(name); }
+  attribute_proxy<V> attr(const char* name) { return attribute_proxy<V>(vector_, name); }
 
-  attribute_proxy<V> attr(const std::string& name) { return vector_.attr(name); }
+  attribute_proxy<V> attr(const std::string& name) {
+    return attribute_proxy<V>(vector_, name.c_str());
+  }
 
-  attribute_proxy<V> attr(SEXP name) { return vector_.attr(name); }
+  attribute_proxy<V> attr(SEXP name) { return attribute_proxy<V>(vector_, name); }
 
   void attr(const char* name, SEXP value) { vector_.attr(name) = value; }