Adapt to SquashService#initialize

What does this MR do and why?

Fix failed pipeline: https://jihulab.com/gitlab-cn/gitlab/-/pipelines/1440107

Why

Upstream 修改了构造函数的入参 merge_requests/128352。

Before

module MergeRequests
  class BaseService < ::IssuableBaseService
    def initialize(project:, current_user: nil, params: {})

After

module MergeRequests
  class SquashService
    def initialize(merge_request:, current_user:, commit_message:)

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Before	After

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