Simplify bench job summary

[xcoulon]

Use the new $GITHUB_STEP_SUMMARYenvironment variable to provide a summary of the bench.
Also, remove the step which publishes the summary using marocchino/sticky-pull-request-comment@v2 and use a regular pull_request trigger instead of pull_request_target

See https://github.blog/2022-05-09-supercharging-github-actions-with-job-summaries/