Don't cast GtkWrapMode to the incompatible enum PangoWrapMode

The enum values are not compatible, and moreover, there is an extra GTK_WRAP_NONE that PangoWrapMode doesn't have - thus, pango_wrap_mode_to_string() will assert.

As far as I can tell, Orca does not read the wrap-mode key in the dictionary for text attributes, anyway.

Fixes: #4869 (closed)

WORK IN PROGRESS: can someone please help me figure this out?

(/builds/federico/gtk/_build/testsuite/gtk/textbuffer:30083): GLib-GObject-CRITICAL **: 23:14:38.363: g_object_ref: assertion '!object_already_finalized' failed

That's in my test's g_assert_finalize_object (buffer) 😓

Figured it out; I was not supposed to unref the text tag 🙃