ci: Some minor speedups to the pipeline
Use all available cores for xz decompression.
Use md5sum instead of sha256sum, as it runs about twice as quickly. The hash is used here to identify the image under test, not for anything related to security.
Use all available cores for xz decompression.
Use md5sum instead of sha256sum, as it runs about twice as quickly. The hash is used here to identify the image under test, not for anything related to security.