ART: Fix oat_writer_test.

Use oat file names with .oat extension, so that
ReplaceFileExtension() used for opening the associated
vdex file does not replace everything starting from the
.temp folder.

bug: 77853712

Test: m test-art-host-gtest-oat_writer_test

(cherry picked from commit f0499c9007d6d74963a10d44e9b1494f7c49febb)

Change-Id: Ic55673f72f7651dd2dbe6b4d34ef2916380f2c75
1 file changed