Add .fa icon margin like .octicon

[sapk]

A little margin is missing for fa icon like openid on this example.
This PR simply duplicate the rule applied on .octicon to .fa

Before

After

[codecov-io]

Codecov Report

Merging #7258 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7258      +/-   ##
==========================================
+ Coverage   40.99%   40.99%   +<.01%     
==========================================
  Files         462      462              
  Lines       62578    62578              
==========================================
+ Hits        25651    25654       +3     
+ Misses      33566    33561       -5     
- Partials     3361     3363       +2

Impacted Files	Coverage Δ
modules/log/file.go	75.52% <0%> (-2.1%)	⬇️
modules/log/event.go	64.61% <0%> (-1.03%)	⬇️
models/repo_list.go	73.09% <0%> (+1.01%)	⬆️
routers/repo/view.go	43.25% <0%> (+1.01%)	⬆️
models/unit.go	67.56% <0%> (+5.4%)	⬆️

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[lunny]

Could you send back port to v1.8 ?