[bitnami/airflow] Improve Goss tests

[juan131]

Description of the change

This PR improves Goss testing for Airflow and fixes an issue on chart metadata.

Benefits

Better test suite

Possible drawbacks

None

Applicable issues

None

Additional information

N/A

Checklist

• [x] Chart version bumped in Chart.yaml according to semver. This is not necessary when the changes only affect README.md files.
• [] Variables are documented in the values.yaml and added to the README.md using readme-generator-for-helm
• [x] Title of the pull request follows this pattern [bitnami/] Descriptive title
• [x] All commits signed off and in agreement of Developer Certificate of Origin (DCO)