Fix build with libc++19; backported from openmw-0.49.0

Index: components/to_utf8/to_utf8.cpp
--- components/to_utf8/to_utf8.cpp.orig
+++ components/to_utf8/to_utf8.cpp
@@ -52,7 +52,7 @@ namespace
         return std::find_if(input.begin(), input.end(), [] (unsigned char v) { return v == 0 || v >= 128; });
     }
 
-    std::basic_string_view<signed char> getTranslationArray(FromType sourceEncoding)
+    std::span<const signed char> getTranslationArray(FromType sourceEncoding)
     {
         switch (sourceEncoding)
         {
