Fix regex to fetch cleaned stacktrace

What does this MR do and why?

Relates to: gitlab-org/quality/quality-engineering/team-tasks#2272 (closed)

In issues like this the regex will consider text from outside the stacktrace too because Rails API section also has (```).

Fix implemented in this MR:

In order to successfully match the stack trace regex (from existing issues), we are now making an assumption that the failure issues which exist already, have a following section (such as Screenshot/Reports) with a ### pattern after Stack trace section.

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

exe/relate-failure-issue --base-issue-labels "Quality,QA" --input-files "/Users/harshamuralidhar/Downloads/rspec-tests.json" --system-log-files "/Users/harshamuralidhar/Downloads/system_log.log" --project "gitlab-org/gitlab" --token "token"

MR acceptance checklist

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