build: fix gtkdragicon header installation

gtk/meson.build

@@ -102,7 +102,6 @@ gtk_private_sources = files([
   'gtkcssvalue.c',
   'gtkcsswidgetnode.c',
   'gtkcustomlayout.c',
-  'gtkdragicon.c',
   'gtkfilechooserembed.c',
   'gtkfilechooserentry.c',
   'gtkfilechoosererrorstack.c',
@@ -214,6 +213,7 @@ gtk_public_sources = files([
   'gtkcssprovider.c',
   'gtkdialog.c',
   'gtkdragdest.c',
+  'gtkdragicon.c',
   'gtkdragsource.c',
   'gtkdrawingarea.c',
   'gtkeditable.c',
@@ -472,6 +472,7 @@ gtk_public_headers = files([
   'gtkdebug.h',
   'gtkdialog.h',
   'gtkdragdest.h',
+  'gtkdragicon.h',
   'gtkdragsource.h',
   'gtkdrawingarea.h',
   'gtkeditable.h',