Activate external_sources for shellcheck in CI

Author: sachilles

.circleci/config.yml

@@ -286,6 +286,7 @@ workflows:
       - shellcheck/check:
           name: shellcheck
           exclude: SC2086,SC2181
+          external_sources: true
           filters:
             tags:
               only: /^([0-9]+)\.([0-9]+)\.([0-9]+)(?:-([0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*))?(?:\+[0-9A-Za-z-]+)?$/