[internal] Add comment for Codspeed triggers

[oliviertassinari]

By default, the pull_request type has opened, synchronize, reopened https://docs.github.com/en/actions/reference/workflows-and-actions/events-that-trigger-workflows#pull_request_target. It seems to be all we need. I was surprised to see this action trigger when a label was applied. It was added in #13952. https://codspeed.io/docs/integrations/ci/github-actions says nothing about it either.

Add comments to clarify why.

[mui-bot]

Deploy preview: https://deploy-preview-19302--material-ui-x.netlify.app/

Bundle size report

Bundle	Parsed size	Gzip size
@mui/x-data-grid	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-pro	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-premium	0B(0.00%)	0B(0.00%)
@mui/x-charts	0B(0.00%)	0B(0.00%)
@mui/x-charts-pro	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers-pro	0B(0.00%)	0B(0.00%)
@mui/x-tree-view	0B(0.00%)	0B(0.00%)
@mui/x-tree-view-pro	0B(0.00%)	0B(0.00%)

Details of bundle changes

Generated by 🚫 dangerJS against d7383fd

[codspeed-hq]

CodSpeed Performance Report

Merging #19302 will not alter performance

_{Comparing oliviertassinari:simpler-codspeed-setup (d7383fd) with master (a937dc5)¹}

Summary

✅ 10 untouched benchmarks

Footnotes

1. No successful run was found on master (edd5484) during the generation of this report, so a937dc5 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[JCQuintas]

@oliviertassinari this action checks for scope: charts label. I've left a comment on the file itself explaining the checks, as the conditional is a bit extensive.

Without labeled, L2 wouldn't work.

    # L1: Run the benchmarks for pushes to the master or next branch and if the changes are in the charts package based on on.push.paths
    # L2: Run the benchmarks if we add the label 'scope: charts' to the pull request
    # L3: Run the benchmarks for pull requests with the label 'scope: charts'
    # Yaml syntax looks a little weird, but it is correct.