urweb: Fix icu headers include path

Since https://github.com/NixOS/nixpkgs/pull/62266
urweb fails to resolve <unicode/utypepes.h> in runtime (during
compilation of project).
upstream commit: https://github.com/urweb/urweb/commit/c2a217f9121dd865122bc6150c53e77bd662050d

resolves #79218

pkgs/development/compilers/urweb/default.nix

@@ -23,6 +23,7 @@ stdenv.mkDerivation rec {
     export PGHEADER="${postgresql}/include/libpq-fe.h";
     export MSHEADER="${libmysqlclient}/include/mysql/mysql.h";
     export SQHEADER="${sqlite.dev}/include/sqlite3.h";
+    export ICU_INCLUDES="-I${icu.dev}/include";
 
     export CC="${gcc}/bin/gcc";
     export CCARGS="-I$out/include \