docs/data/reusables/actions/reusable-workflow-calling-syntax.md

• {owner}/{repo}/.github/workflows/{filename}@{ref} for reusable workflows in {% ifversion fpt %}public and private{% elsif ghec or ghes > 3.7 or ghae > 3.7 %}public, internal and private{% else %}public and internal{% endif %} repositories.
• ./.github/workflows/{filename} for reusable workflows in the same repository.

In the first option, {ref} can be a SHA, a release tag, or a branch name. If a release tag and a branch have the same name, the release tag takes precedence over the branch name. Using the commit SHA is the safest option for stability and security. For more information, see "AUTOTITLE."

If you use the second syntax option (without {owner}/{repo} and @{ref}) the called workflow is from the same commit as the caller workflow. Ref prefixes such as refs/heads and refs/tags are not allowed.