deprecating span::at and span::operator()

tests/span_tests.cpp

@@ -17,8 +17,11 @@
 #ifdef _MSC_VER
 // blanket turn off warnings from CppCoreCheck from catch
 // so people aren't annoyed by them when running the tool.
-#pragma warning(disable : 26440 26426 26497 4189) // from catch
+#pragma warning(disable : 26440 26426 26497 4189 4996)
 
+#if __clang__ || __GNUC__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 #endif
 
 #if __clang__ || __GNUC__