Fix mr pipeline detection for child pipelines

[andrcuns]

When pipeline on Gitlab CI is a child pipeline, pipeline_source will not be merge_request_pipeline. Switch to checking for mr_iid as a more reliable way of detecting mr context

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Test Report

allure-report-publisher generated test report!

rspec: ✅ test report for 04192682

+----------------------------------------------------------------+
|                       behaviors summary                        |
+-----------+--------+--------+---------+-------+-------+--------+
|           | passed | failed | skipped | flaky | total | result |
+-----------+--------+--------+---------+-------+-------+--------+
| helpers   | 129    | 0      | 0       | 0     | 129   | ✅     |
| commands  | 93     | 0      | 0       | 0     | 93    | ✅     |
| uploaders | 51     | 0      | 0       | 0     | 51    | ✅     |
| providers | 69     | 0      | 0       | 0     | 69    | ✅     |
| cli       | 3      | 0      | 0       | 0     | 3     | ✅     |
| generator | 6      | 0      | 0       | 0     | 6     | ✅     |
+-----------+--------+--------+---------+-------+-------+--------+
| Total     | 351    | 0      | 0       | 0     | 351   | ✅     |
+-----------+--------+--------+---------+-------+-------+--------+

[codeclimate]

Code Climate has analyzed commit 0419268 and detected 0 issues on this pull request.

The test coverage on the diff in this pull request is 100.0% (50% is the threshold).

This pull request will bring the total coverage in the repository to 97.8% (0.0% change).

View more on Code Climate.