E2E test user cancels MR in merge trains doesn't create To-Do item

Description of the test

When a merge train starts but user cancel any merge request in that trains by clicking the cancel auto merge button, this action will not create any new To-Do item.

Test case gitlab-org/quality/testcases#1044 (closed)

• Refactor existing test, rename from system_cancels_merge_request_in_merge_trains_spec.rb to cancelling_merge_request_in_merge_trains_spec.rb.
• Adding this as the 2nd example to the test to minimize set up time.
• Note the 1st example is still under quarantine due to bug.
• Also needed to update snapshot file to help FE test pass.

Check-list

• Confirm the test has a testcase: tag linking to an existing test case in the test case project.
• Note if the test is intended to run in specific scenarios. If a scenario is new, add a link to the MR that adds the new scenario.
• Follow the end-to-end tests style guide and best practices.
• Use the appropriate RSpec metadata tag(s).
• Ensure that a created resource is removed after test execution. A Group resource can be shared between multiple tests. Do not remove it unless it has a unique path. Note that we have a cleanup job that periodically removes groups under gitlab-qa-sandbox-group.
• Ensure that no transient bugs are hidden accidentally due to the usage of waits and reloads.
• Verify the tags to ensure it runs on the desired test environments.
• If this MR has a dependency on another MR, such as a GitLab QA MR, specify the order in which the MRs should be merged.
• (If applicable) Create a follow-up issue to document the special setup necessary to run the test: ISSUE_LINK