Fix http path retrievals

[hannahhoward]

Goals

Well folks, I guess this is why we integration test. Looks like we had a very missing trailing slash in the HTTP retrievals which will cause everything except for root cid retrievals to fail.

Implementation

• Fix it
• Add integrations tests we never quite got to that sadly, probably would have caught this one

[codecov-commenter]

Codecov Report

Merging #270 (b862c5d) into main (d87d939) will increase coverage by 0.43%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #270      +/-   ##
==========================================
+ Coverage   70.85%   71.28%   +0.43%     
==========================================
  Files          71       71              
  Lines        6179     6179              
==========================================
+ Hits         4378     4405      +27     
+ Misses       1551     1531      -20     
+ Partials      250      243       -7     

Impacted Files	Coverage Δ
pkg/retriever/httpretriever.go	84.95% <100.00%> (ø)

... and 11 files with indirect coverage changes