fix: 修复 DAG 环路检测

[1005281342]

有 spec 如下:

steps:
  - name: a
    command: echo hello

  - name: b
    command: echo hello
    depends:
      - a

  - name: c
    command: echo hello
    depends:
      - b

  - name: d
    command: echo hello
    depends:
      - b

  - name: e
    command: echo hello
    depends:
      - f

  - name: g
    command: echo hello
    depends:
      - f
      - b

  - name: h
    command: echo hello
    depends:
      - e
      - g
      - f

  - name: i
    command: echo hello
    depends:
      - f


  - name: j
    command: echo hello
    depends:
      - f

  - name: f
    command: echo hello
    depends:
      - d

  - name: k
    command: echo hello
    depends:
      - b

  - name: o
    command: echo hello
    depends:
      - b

  - name: p
    command: echo hello
    depends:
      - b

  - name: q
    command: echo hello
    depends:
      - b
      - f
      - k
      - o
      - p

当前版本(v1.10.3)，提示 cycle detected：

本次提交修复后：

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.07 🎉

Comparison is base (b0a4fd8) 81.25% compared to head (73bc2e2) 81.32%.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main     #427      +/-   ##
==========================================
+ Coverage   81.25%   81.32%   +0.07%     
==========================================
  Files          30       30              
  Lines        3345     3358      +13     
==========================================
+ Hits         2718     2731      +13     
  Misses        488      488              
  Partials      139      139              

Impacted Files	Coverage Δ
internal/scheduler/graph.go	80.91% <100.00%> (+2.10%)	⬆️

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[yohamta]

@1005281342 Great work on fixing the bug in the cycle detection code! Your contribution is greatly appreciated and will ensure the reliability and stability of Dagu. Thank you for taking the time to investigate and resolve the issue. Keep up the good work!