gitGraph: merge commit improvment

[macherel]

Description

Some merge commits are not displayed properly.

Steps to reproduce

Create a merge commit with gitGraph.
The graph is not displayed properly.

Screenshots

Code Sample

gitGraph LR:
  commit

  branch branch-A
  commit
  merge main

  checkout main
  commit
  checkout branch-A
  merge main

gitGraph LR:
  commit

  branch branch-A
  commit
  merge main

  checkout main
  commit
  checkout branch-A
  merge main

gitGraph LR:
  commit

  branch branch-A
  branch branch-B
  commit

  checkout branch-A
  merge branch-B

  checkout branch-B
  merge branch-A

gitGraph LR:
  commit

  branch branch-A
  branch branch-B
  commit

  checkout branch-A
  merge branch-B

  checkout branch-B
  merge branch-A

gitGraph LR:
  commit

  branch branch-B order: 2
  commit

  branch branch-A
  merge main

  checkout branch-B
  merge branch-A

gitGraph LR:
  commit

  branch branch-B order: 2
  commit

  branch branch-A
  merge main

  checkout branch-B
  merge branch-A

Setup

• Mermaid version: latest develop
• Browser and Version: [Chrome, Edge, Firefox]

Suggested Solutions

Proposal made in the PR #5152

Additional Context

No response