sharing: Add missing widget cast

Was missed in a5de11c3.
11 jobs for sharing-missing-case in 2 minutes and 34 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #608012
build

00:01:44

 
  Test
passed #608013
test

00:00:50

 
  Manual
manual #608019
allowed to fail manual
armv8
manual #608015
allowed to fail manual
asan
manual #608014
allowed to fail manual
flatpak
manual #608018
allowed to fail manual
msan
manual #608020
allowed to fail manual
ppc64le
manual #608016
allowed to fail manual
tsan
manual #608017
allowed to fail manual
ubsan
 
  Review
manual #608021
allowed to fail manual
review
manual #608022
allowed to fail manual
stop_review