community/pidgin-sipe: fix build with gcc 14
Fix -Wincompatible-pointer-types
error with gcc 14 (rebuild error log on loongarch64).
sipe-xml.c:210:9: error: initialization of 'void (*)(void *, const xmlError *)' {aka 'void (*)(void *, const struct _xmlError *)'} from incompatible pointer type 'void (*)(void *, xmlError *)' {aka 'void (*)(void *, struct _xmlError *)'} [-Wincompatible-pointer-types]
210 | callback_serror, /* serror */
| ^~~~~~~~~~~~~~~
sipe-xml.c:210:9: note: (near initialization for 'parser.serror')
sipe-xml.c: In function 'sipe_xml_parse':
sipe-xml.c:220:17: warning: 'xmlSAXUserParseMemory' is deprecated [-Wdeprecated-declarations]
220 | if (xmlSAXUserParseMemory(&parser, pd, string, length))
| ^~
In file included from sipe-xml.c:31:
/usr/include/libxml2/libxml/parser.h:1010:17: note: declared here
1010 | xmlSAXUserParseMemory (xmlSAXHandlerPtr sax,
| ^~~~~~~~~~~~~~~~~~~~~