community/vorbis-tools: fix build with gcc 14
Fix -Wimplicit-function-declaration
error with gcc 14.
Error:
codec_skeleton.c: In function 'skeleton_process_fisbone_message_header':
codec_skeleton.c:119:9: error: implicit declaration of function 'utf8_decode' [-Wimplicit-function-declaration]
119 | if (utf8_decode(header, &decoded) < 0) {
| ^~~~~~~~~~~