Metric reports do not support tags

Summary

Creating a metric report (using the OpenMetrics format) in a CI job seems to ignore metrics with tags.

Steps to reproduce

Create a CI stage like so:

My Stage:
  image: alpine
  script:
    - echo 'my_metric{tag="1"} 10' > metrics.txt
  artifacts:
    reports:
      metrics: metrics.txt

Open a MR with this. Then, commit a change to the script section:

    - echo 'my_metric{tag="1"} 20' > metrics.txt

Example Project

See this merge request: tom6/metrics-bug!1 (diffs)

What is the current bug behavior?

It says "Metric reports did not change", but that's not correct.

What is the expected correct behavior?

It should notice that the metric my_metric{tag="1"} has changed from 10 to 20.