apt 1.0.9.8.6 gives a 404 error

Trying to build jessie-based debootstrap-image yields the following error:

--2021-02-17 03:56:24--  https://deb.freexian.com/extended-lts/pool/main/a/apt/apt_1.0.9.8.6_amd64.deb
62.210.102.136
Connecting to deb.freexian.com (deb.freexian.com)|62.210.102.136|:443... HTTP request sent, awaiting response... Error: Error downloading file

This is because the apt packages on Freexian have been updated to 1.0.9.8.7 due to CVE-2020-27350, so 1.0.9.8.6 yields a 404 error.

Marking as confidential because there's an apt CVE involved, and I haven't tried to audit whether that vulnerability is dangerous to tor-browser-build.

I will send in a MR shortly.