Last commit to merge-request with skip-ci doesn't run merge pipeline anymore
### Summary
We use merge request to build our official releases. Often we do very small changes at the end on the source branch with [skip-ci] to prevent running all our pipeline twice (pipelines are slow on our codebase ~1hr).
This used to work without issues but as of recent changes on gitlab.com, when I tried it today my pipeline on the release branch just said, "Skipped" (because the last commit probably contained a message with [skip-ci] (single commit merge request).
### Steps to reproduce
Create a branch source.
Merge non-fast-forward into branch release
Make a single change to source with [skip-ci] in the commit message
Merge using merge request into release again.
Note that the pipeline is not run now.
### Example Project
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### What is the current *bug* behavior?
Pipelines are skipped
### What is the expected *correct* behavior?
Pipelines for the result of the merge are still executed
### Relevant logs and/or screenshots
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### Output of checks
This bug happens on GitLab.com
#### Results of GitLab environment info
#### Results of GitLab application Check
### Possible fixes
labels: gitlab-ce~2278648 gitlab-ce~3630472
issue