tests/reflection_test.h: add missing <stdint.h> include

[trofi]

Without the change build fails on weekly gcc-13 snapshots as:

In file included from /build/flatbuffers/tests/reflection_test.cpp:1:
tests/reflection_test.h:9:57: error: 'uint8_t' has not been declared
    9 | void ReflectionTest(const std::string& tests_data_path, uint8_t *flatbuf, size_t length);
      |                                                         ^~~~~~~

[enum-class]

This type is defined in the C header <stdint.h> which is part of the C++ standard sice 2011, is it necessary to import it?

[trofi]

Before C++11 you could not reliably include it as it was not a standard header. From C++11 on you can and should include it if you want to pull uint8_t into scope: stdint.h for global scope, <cstdint> for std:: scope. Standard defines the header as https://en.cppreference.com/w/cpp/types/integer

It's still not a fundamental type like int or wchar_t. Those would not require any headers. Standard defines list of fundamental types as https://en.cppreference.com/w/cpp/language/types