fix int

Fixed

[2153/2321] Compiling C object app/widgets/libappwidgets.a.p/gimppanedbox.c.o
../app/widgets/gimppanedbox.c: In function ‘gimp_paned_box_dispose’:
../app/widgets/gimppanedbox.c:171:17: warning: comparison of integer expressions of different signedness: ‘gint’ {aka ‘int’} and ‘long unsigned int’ [-Wsign-compare]
  171 |   for (i = 0; i < G_N_ELEMENTS (paned_box->p->dnd_highlights); i++)
      |                 ^
../app/widgets/gimppanedbox.c: In function ‘gimp_paned_box_drop_indicator_draw’:
../app/widgets/gimppanedbox.c:370:17: warning: comparison of integer expressions of different signedness: ‘gint’ {aka ‘int’} and ‘long unsigned int’ [-Wsign-compare]
  370 |   for (i = 0; i < G_N_ELEMENTS (paned_box->p->dnd_highlights); i++)
      |                 ^