Workaround for posting single comments in split diff view

[rfwatson]

Workaround for #4745.

• This doesn't fix the root cause, which is that the .add-code-comment div is somehow obscuring the Post single comment button and hijacking the click events
• Changing the button's z-index doesn't seem to have an effect
• It's not clear why the other buttons on the same form aren't affected 🤷‍♂️

[rfwatson]

Not sure why the CI is failing

[lunny]

It's unrelated, restarted.

[codecov-io]

Codecov Report

Merging #7052 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #7052      +/-   ##
==========================================
+ Coverage   41.44%   41.45%   +0.01%     
==========================================
  Files         442      442              
  Lines       59604    59608       +4     
==========================================
+ Hits        24702    24713      +11     
+ Misses      31672    31664       -8     
- Partials     3230     3231       +1

Impacted Files	Coverage Δ
models/models.go	57.5% <0%> (+0.72%)	⬆️
routers/repo/view.go	43.03% <0%> (+1.01%)	⬆️
modules/log/colors_router.go	87.5% <0%> (+4.16%)	⬆️
models/unit.go	67.56% <0%> (+5.4%)	⬆️

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[zeripath]

Make lg-tm work