Update vendor/libarchive to git b3bd0b81a1a06909f766dea8be4072ef81de62b8
Vendor bugfixes:
cpio reader sanity fix (OSS-Fuzz 504)
WARC reader sanity fixes (OSS-Fuzz 511, 526, 532, 552)
mtree reader time parsing fix (OSS-Fuzz 538)
XAR reader memleak fix (OSS-Fuzz 551)