Make iterator_proxy_value a forward_iterator (#4371) (#4372)

* Make iteration_proxy_value model forward_iterator

* Amalgamate

* Suppress tidy warning

include/nlohmann/detail/iterators/iteration_proxy.hpp

@@ -9,7 +9,7 @@
 #pragma once
 
 #include <cstddef> // size_t
-#include <iterator> // input_iterator_tag
+#include <iterator> // forward_iterator_tag
 #include <string> // string, to_string
 #include <tuple> // tuple_size, get, tuple_element
 #include <utility> // move
@@ -40,7 +40,7 @@ template<typename IteratorType> class iteration_proxy_value
     using value_type = iteration_proxy_value;
     using pointer = value_type *;
     using reference = value_type &;
-    using iterator_category = std::input_iterator_tag;
+    using iterator_category = std::forward_iterator_tag;
     using string_type = typename std::remove_cv< typename std::remove_reference<decltype( std::declval<IteratorType>().key() ) >::type >::type;
 
   private:

single_include/nlohmann/json.hpp

@@ -5181,7 +5181,7 @@ NLOHMANN_JSON_NAMESPACE_END
 
 
 #include <cstddef> // size_t
-#include <iterator> // input_iterator_tag
+#include <iterator> // forward_iterator_tag
 #include <string> // string, to_string
 #include <tuple> // tuple_size, get, tuple_element
 #include <utility> // move
@@ -5215,7 +5215,7 @@ template<typename IteratorType> class iteration_proxy_value
     using value_type = iteration_proxy_value;
     using pointer = value_type *;
     using reference = value_type &;
-    using iterator_category = std::input_iterator_tag;
+    using iterator_category = std::forward_iterator_tag;
     using string_type = typename std::remove_cv< typename std::remove_reference<decltype( std::declval<IteratorType>().key() ) >::type >::type;
 
   private:

tests/src/unit-readme.cpp

@@ -171,7 +171,7 @@ TEST_CASE("README" * doctest::skip())
 
             // find an entry
             CHECK(o.find("foo") != o.end());
-            if (o.find("foo") != o.end())
+            if (o.find("foo") != o.end()) // NOLINT(readability-container-contains)
             {
                 // there is an entry with key "foo"
             }