oe/sdk: fix empty SDK manifests

oe/sdk: fix empty SDK manifests

The SDK manifests are generated by listing the sstate was that used, but
it hardcodes that the sstate data filenames end in .tgz.

This has not been the case since sstate switched to Zstd[1] in 2021,
which meant that all of the tests which checked for packages existing
were being skipped as the manifests were empty.  For example, see a
representative core-image-sato eSDK test run[2]:

RESULTS - cmake.CMakeTest.test_assimp: SKIPPED (0.00s)
RESULTS - gtk3.GTK3Test.test_galculator: SKIPPED (0.00s)
RESULTS - kmod.KernelModuleTest.test_cryptodev: SKIPPED (0.00s)
RESULTS - maturin.MaturinDevelopTest.test_maturin_develop: SKIPPED (0.00s)
RESULTS - maturin.MaturinTest.test_maturin_list_python: SKIPPED (0.00s)
RESULTS - meson.MesonTest.test_epoxy: SKIPPED (0.00s)
RESULTS - perl.PerlTest.test_perl: SKIPPED (0.00s)
RESULTS - python.Python3Test.test_python3: SKIPPED (0.00s)

All of those tests should have been ran.

Solve this by generalising the filename check so that it doesn't care
what specfic compression algorithm is used.

[1] oe-core 0710e98f40e ("sstate: Switch to ZStandard compressor support")
[2] https://autobuilder.yoctoproject.org/valkyrie/#/builders/16/builds/1517/steps/15/logs/stdio

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Peter Marko <peter.marko@siemens.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>