The $GITHUB_ENV environment variable is used to set environment variables that persist across steps in a workflow job. By echoing FOO=bar into $GITHUB_ENV, the variable FOO will be available in subsequent steps within the same job.
Variables set in GITHUB_ENV apply only to the current job.
Example:
echo "PR_NUMBER=$pr_number" >> $GITHUB_ENV
Reference:
https://github.com/orgs/community/discussions/56849