Add missing include

In file included from /home/elsid/dev/openmw/apps/openmw_test_suite/settings/testvalues.cpp:1:
/home/elsid/dev/openmw/components/misc/strings/conversion.hpp: In function ‘std::string Misc::StringUtils::toHex(std::string_view)’:
/home/elsid/dev/openmw/components/misc/strings/conversion.hpp:139:87: error: ‘uint8_t’ in namespace ‘std’ does not name a type; did you mean ‘wint_t’?
  139 |             const std::ptrdiff_t space = static_cast<std::ptrdiff_t>(static_cast<std::uint8_t>(v) <= 0xf);
      |                                                                                       ^~~~~~~
      |                                                                                       wint_t
/home/elsid/dev/openmw/components/misc/strings/conversion.hpp:140:97: error: ‘uint8_t’ in namespace ‘std’ does not name a type; did you mean ‘wint_t’?
  140 |             const auto [ptr, ec] = std::to_chars(out + space, out + space + 2, static_cast<std::uint8_t>(v), 16);
      |                                                                                                 ^~~~~~~
      |                                                                                                 wint_t

components/misc/strings/conversion.hpp

@@ -2,6 +2,7 @@
 #define COMPONENTS_MISC_STRINGS_CONVERSION_H
 
 #include <charconv>
+#include <cstdint>
 #include <optional>
 #include <string>
 #include <system_error>