test_arch_work_dir_and_export_source uses the archiver to generate SRPMS,
so explicitly set PACKAGE_CLASSES to ensure that package_rpm is used.
(From OE-Core rev: 030157fa8dd405be60c55523e074b2ec950d36ad)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>