[gimp] libgimpwidgets: fix the def file.

[Jehan <jehanp src gnome org>]

commit 60b67ec2046b0d7d8cfc0c7cb7106ca0b3170cb3
Author: Jehan <jehan girinstud io>
Date:   Sun Mar 6 00:35:32 2022 +0100

    libgimpwidgets: fix the def file.
    
    The gimp_widget_set_identifier() doesn't really need to be there since
    we don't install the gimpwidgets-private.h header. But I guess it makes
    sense that we still need to add it for our internal use at least.
    
    This should fix the CI.

 libgimpwidgets/gimpwidgets.def | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/libgimpwidgets/gimpwidgets.def b/libgimpwidgets/gimpwidgets.def
index 6e85834228..906a0936b9 100644
--- a/libgimpwidgets/gimpwidgets.def
+++ b/libgimpwidgets/gimpwidgets.def
@@ -475,6 +475,7 @@ EXPORTS
        gimp_widget_get_color_profile
        gimp_widget_get_color_transform
        gimp_widget_get_monitor
+       gimp_widget_set_identifier
        gimp_widget_track_monitor
        gimp_widgets_error_quark
        gimp_widgets_init