Close resources left by go-git after request is finished

[Sebazzz]

Rebase of #8915 onto master

In #7947 I figured out that go-git leaves handles to the pack files open. These are eventually garbage collected, but this isn't very deterministic.

What I did:

• Close any open repository handles after each request via a common middleware so it is on one place instead of littered throughout the source code. (There might still be a possible race condition here if many concurrent page views are happening on the repository and a transfer ownership or rename is attempted)
• Close the repository before ownership transfer or rename which are the operations that touch the directory.
• Log if closing the repository fails, apparently go-git can return an error.
• Tested on Windows based on the testcase in Transfer the ownership 转移仓库所有权 do not work in V1.90~V1.92 #7947 as I'm a Windows user.

I believe this should be quite easy to merge and addresses all issues when it comes to resources left open by requests.

[codecov-io]

Codecov Report

Merging #8916 into master will increase coverage by <.01%.
The diff coverage is 48%.

@@            Coverage Diff             @@
##           master    #8916      +/-   ##
==========================================
+ Coverage    41.3%   41.31%   +<.01%     
==========================================
  Files         545      545              
  Lines       70368    70393      +25     
==========================================
+ Hits        29068    29080      +12     
- Misses      37601    37611      +10     
- Partials     3699     3702       +3

Impacted Files	Coverage Δ
routers/repo/setting.go	13.13% <0%> (-0.2%)	⬇️
modules/git/repo.go	56.79% <100%> (+0.42%)	⬆️
routers/routes/routes.go	82.61% <100%> (+0.04%)	⬆️
modules/context/context.go	50.22% <72.72%> (+1.17%)	⬆️
models/unit.go	62.16% <0%> (-5.41%)	⬇️
modules/migrations/migrate.go	21.22% <0%> (-1.68%)	⬇️
modules/migrations/gitea.go	8.05% <0%> (-0.64%)	⬇️
models/repo.go	49.07% <0%> (-0.06%)	⬇️
models/error.go	33.86% <0%> (+1.18%)	⬆️
modules/task/migrate.go	28.94% <0%> (+3.94%)	⬆️

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