feat: cancel the previous run when a new event occurs for the same PR

[wwcchh0123]

fix #177

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[codecov]

Codecov Report

Attention: Patch coverage is 8.88889% with 41 lines in your changes missing coverage. Please review.

Project coverage is 35.75%. Comparing base (878265c) to head (75e59b4).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
server.go	0.00%	16 Missing ⚠️
internal/linters/linters.go	0.00%	7 Missing ⚠️
internal/storage/file.go	50.00%	3 Missing and 1 partial ⚠️
internal/linters/github.go	0.00%	3 Missing ⚠️
internal/linters/go/golangci_lint/golangci_lint.go	0.00%	2 Missing ⚠️
internal/linters/c/cppcheck/cppcheck.go	0.00%	1 Missing ⚠️
internal/linters/doc/note-check/note.go	0.00%	1 Missing ⚠️
internal/linters/go/gofmt/gofmt.go	0.00%	1 Missing ⚠️
internal/linters/go/gomodcheck/gomodcheck.go	0.00%	1 Missing ⚠️
internal/linters/go/staticcheck/staticcheck.go	0.00%	1 Missing ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #386      +/-   ##
==========================================
- Coverage   36.01%   35.75%   -0.27%     
==========================================
  Files          27       27              
  Lines        2335     2358      +23     
==========================================
+ Hits          841      843       +2     
- Misses       1369     1390      +21     
  Partials      125      125              

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[CarlJi]

这一句在这里应该没意义

[CarlJi]

defer 里面单纯的加个 delete 逻辑就好，应该不需要select

[wwcchh0123]

当前一个事件的ctx 被取消，还是会执行defer func 内容，若不加 select ，即每次都会进行delete删除，导致该PR map内容为空，不符合预期