BOM in included CI files causes jobs to be excluded from the pipeline

Summary

Included CI files containing the UTF-8 Byte-Order Mark (BOM) causes files to be partially parsed and jobs are missing from the pipeline.

Potentially related to our handling of the BOM reported on #353946 (closed) but in this case the pipeline does not fail.

Steps to reproduce

1. Create a gitlab-ci.yml file on a project, including another files via the include: clause.
2. Add the BOM to the included file.
3. Run a pipeline.
4. The pipeline succeeds but some jobs are not included.

Example Project

This pipeline shows the erratic behavior. Only jobA is included in the pipeline while jobB is missing.

What is the current bug behavior?

Jobs are not included in the pipeline.

What is the expected correct behavior?

All jobs in the included files should be added to the pipeline.

Output of checks

This bug happens on GitLab.com.

Possible fixes