The textbuffer test is calling into a function defined by the AT-SPI
accessibility backend. As of commit 4ddf1b70 we only build and run the
test on Linux, but the function in question isn't really
accessibility-related: it's just a serialization function.
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
