Draft: community/php83: use gnu-libiconv for iconv

Uses https://github.com/php/php-src/commit/b480e6841ecd5317faa136647a2b8253a4c2d0df (as it is alpine aware already :)).

Trys to fix #12328 (closed) and #15114. Maybe related to #15603

There is also an open ticket at https://github.com/php/php-src/issues/12213 (which says alpine should work with --with-iconv=/usr - which does not :().