Fix: Replace all references to debian 8 with 11

[reglim]

Fixes #1218

Requirements

All new code should be covered with tests, documentation should be updated. CI should pass.

Description of the Change

Updated the repo key, repo links in tests (jessie-cran35 -> bullseye-cran40) and the expected test output.

Why this change is important?

The CI should pass

Checklist

• unit-test added (if change is algorithm)
• functional test added/updated (if change is functional)
• man page updated (if applicable)
• bash completion updated (if applicable)
• documentation updated
• author name in AUTHORS

[randombenj]

LGTM

[codecov]

Codecov Report

Merging #1215 (3ae5144) into master (1df8cff) will decrease coverage by 0.04%.
Report is 6 commits behind head on master.
The diff coverage is 57.14%.

@@            Coverage Diff             @@
##           master    #1215      +/-   ##
==========================================
- Coverage   65.99%   65.96%   -0.04%     
==========================================
  Files         143      143              
  Lines       16196    16190       -6     
==========================================
- Hits        10688    10679       -9     
- Misses       4754     4758       +4     
+ Partials      754      753       -1     

Files Changed	Coverage Δ
api/mirror.go	14.78% <0.00%> (ø)
deb/graph.go	0.00% <0.00%> (ø)
api/task.go	42.15% <100.00%> (ø)
deb/import.go	76.50% <100.00%> (+0.92%)	⬆️

... and 2 files with indirect coverage changes

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