www/webkit2-gtk*: Fix build with ICU 76.1
Backport upstream commit aa29001ade54425699e1345ce41bbd227dba805c
Reference:
https://github.com/WebKit/WebKit/commit/aa29001ade54425699e1345ce41bbd227dba805c
PR: 283578, 283579
Approved by: portmgr (blanket)