gtk: fix GtkPasswordEntryBuffer introspection

Move the source file to public_sources list, and fix tag annotation.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

gtk/gtkpasswordentrybuffer.c

@@ -38,7 +38,7 @@
  *
  * `GtkPasswordEntry` uses a `GtkPasswordEntryBuffer`.
  *
- * Since 4.4.
+ * Since: 4.4
  */
 struct _GtkPasswordEntryBuffer
 {

gtk/meson.build

@@ -123,7 +123,6 @@ gtk_private_sources = files([
   'gtkpanedhandle.c',
   'gtkpango.c',
   'gskpango.c',
-  'gtkpasswordentrybuffer.c',
   'gtkpathbar.c',
   'gtkplacessidebar.c',
   'gtkplacesview.c',
@@ -325,6 +324,7 @@ gtk_public_sources = files([
   'gtkpaned.c',
   'gtkpapersize.c',
   'gtkpasswordentry.c',
+  'gtkpasswordentrybuffer.c',
   'gtkpicture.c',
   'gtkpopover.c',
   'gtkpopovermenu.c',