fix: catch server stop error

[charviki]

Description (what this PR does / why we need it):

问题：服务在收到 os.Signal 后退出，但并未返回服务在关闭过程中出现的错误。
原因：在 errgroup 中返回了 ctx.Err()。按照原有的代码逻辑，如果不考虑极端情况，在收到 os.Signal 后 errgroup 都会返回 context.Canceled，因为 errgroup 只会返回第一个错误，而 context.Canceled 这个错误在 Run 方法中会被忽略，这就导致了 Run 未捕获到服务关闭过程中的错误。
p.s. 这里把 for 代码也删了，因为考虑到 ctx.Err() 仅会返回 context.Canceled 以及 context.DeadlineExceeded，结合上下文，该 ctx 不会出现超时的情况，所以不需要返回 ctx.Err()。

Which issue(s) this PR fixes (resolves / be part of):

Other special notes for the reviewers:

[codecov-commenter]

Codecov Report

Merging #2125 (4121362) into main (a0e624c) will increase coverage by 0.06%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##             main    #2125      +/-   ##
==========================================
+ Coverage   78.99%   79.06%   +0.06%     
==========================================
  Files          84       84              
  Lines        3699     3697       -2     
==========================================
+ Hits         2922     2923       +1     
+ Misses        564      561       -3     
  Partials      213      213              

Impacted Files	Coverage Δ
app.go	83.83% <60.00%> (+0.67%)	⬆️
internal/context/context.go	100.00% <0.00%> (+2.98%)	⬆️

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