Fix non-determinism of .tar.gz files On CI, the .tar.gz files of the bp2build files have a timestamp in them. Locally, they don't for some reason. I think glinux might be configured somehow to have gzip not output timestamps, but the build servers aren't. Tar does not provide an option to not add a timestamp to the gzip header, so instead gzip the file seperately. Bug: 247785938 Test: Presubmits Change-Id: Ic7c709d9ab6b89f3a02a5a59d1c2349c16caf765