Load Issue attributes for API call

[jolheiser]

Fixes #6056

Issues were being loaded raw instead of with attributes. Changed the API to use the func that loads attributes.

[codecov-io]

Codecov Report

Merging #6122 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #6122      +/-   ##
==========================================
- Coverage   38.85%   38.84%   -0.02%     
==========================================
  Files         352      352              
  Lines       50030    50030              
==========================================
- Hits        19440    19434       -6     
- Misses      27776    27783       +7     
+ Partials     2814     2813       -1

Impacted Files	Coverage Δ
routers/api/v1/repo/issue.go	23.46% <0%> (ø)	⬆️
models/unit.go	0% <0%> (-14.29%)	⬇️
routers/repo/view.go	44.54% <0%> (-1.15%)	⬇️

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[sankethpb]

@lafriks Is there any workaround for this in 1.7.2?
Would be great to have it back ported to 1.7.3, thank you.

[lafriks]

Please backport to 1.7