fix(aws-auth): fix reference to the action's own path (#1032)

This is a workaround for actions/runner#716
(closed but not fixed): use `${GITHUB_ACTION_PATH}` instead of `${{
  github.action_path }}`.

Author: iainlane

actions/aws-auth/action.yaml

@@ -69,6 +69,6 @@ runs:
         if [[ ! -z "${REPOSITORY_PATH}" ]]; then
           cd ${REPOSITORY_PATH}/actions/aws-auth
         else
-          cd "${{ github.action_path }}"
+          cd "${GITHUB_ACTION_PATH}"
         fi
         ./resolve-aws-region.sh