dxf export: recover korean encodings (CP949) (fixes #20838)

(cherry picked from commit 4e74c8b)

Author: jef-n

src/core/dxf/qgsdxfexport.cpp

@@ -356,7 +356,7 @@ const char *QgsDxfExport::DXF_ENCODINGS[][2] =
   { "ANSI_874", "CP874" },
   { "ANSI_932", "Shift_JIS" },
   { "ANSI_936", "CP936" },
-  { "ANSI_949", "cp949" },
+  { "ANSI_949", "CP949" },
   { "ANSI_950", "CP950" },
 //  { "ANSI_1361", "" },
 //  { "ANSI_1200", "" },