Print redirects being followed, drop mirror.yandex.ru.

[smira]

Use CDN-backed Debian mirror to make tests run faster hopefully for
everyone. Redirects might be important to know what exactly is going on
when items are being downloaded.

[codecov]

Codecov Report

Merging #864 into master will decrease coverage by 0.03%.
The diff coverage is 20%.

@@            Coverage Diff             @@
##           master     #864      +/-   ##
==========================================
- Coverage    64.1%   64.06%   -0.04%     
==========================================
  Files          51       51              
  Lines        6560     6565       +5     
==========================================
+ Hits         4205     4206       +1     
- Misses       1850     1854       +4     
  Partials      505      505

Impacted Files	Coverage Δ
http/download.go	78.01% <20%> (-2.14%)	⬇️

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[smira]

Rebased without changes