Stabilize test so it passes on Android too

Android treats "utf-32" as ambiguous with respect to
ordering and so outputs a BOM. utf-32be / utf-32le do
not. Specifying the byte-ordering stabilizes the test
and makes it pass on Android.

Context:

The RI I looked at does not output the BOM for "utf-32".

As comparison: For both, "utf-16" outputs a BOM, and does
not for "utf-16le" / "utf-16be". This is documented. This
inconsistency between "utf-32" and "utf-16" on the RI
suggests the lack of a BOM with is a "feature" of the RI.

When le/be is not specified it is worth noting that Android
and the RI I tried used different ordering, though I did
not check whether the ordering was stable on different
platforms.