Split cancel MR in merge train spec into 2 specs

What does this MR do and why?

Describe in detail what your merge request does and why.

Splitting cancel MR in merge train test cases into their own spec file per discussion #358843 (comment 910600501)

TODO:

• Update test case titles and contents with new file paths after merge.
• https://gitlab.com/gitlab-org/gitlab/-/quality/test_cases/347666
• https://gitlab.com/gitlab-org/gitlab/-/quality/test_cases/347665

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.