Fix the clang-tidy 22 findings in json_view and its tests

The same changes as on the dump branch, where they were first made, so
that this branch passes clang-tidy on its own.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/view/lookup.hpp

@@ -127,7 +127,7 @@ template<typename SizeType, typename IntegerType>
 SizeType to_index(IntegerType idx) noexcept
 {
     const IntegerType zero = 0;
-    const auto result = static_cast<SizeType>(idx);
+    const auto result = static_cast<SizeType>(idx); // NOLINT(bugprone-signed-char-misuse,cert-str34-c): negative values are mapped below
     return (idx < zero || static_cast<IntegerType>(result) != idx) ? (std::numeric_limits<SizeType>::max)() : result;
 }