Merge branch 'ps/weak-sha1-for-tail-sum-fix'

An earlier "csum-file checksum does not have to be computed with sha1dc" topic had a few code paths that had initialized an implementation of a hash function to be used by an unmatching hash by mistake, which have been corrected. * ps/weak-sha1-for-tail-sum-fix: ci: exercise unsafe OpenSSL backend builtin/fast-import: fix segfault with unsafe SHA1 backend bulk-checkin: fix segfault with unsafe SHA1 backend