testing/libosip2: update version to 5.2.0
Generally osip2 and eXosip2 versions need to be kept in sync, especially around major point releases. eXosip2 had already been updated to 5.2.0 by ?? @Leo ??
Generally osip2 and eXosip2 versions need to be kept in sync, especially around major point releases. eXosip2 had already been updated to 5.2.0 by ?? @Leo ??