[bitnami/mongodb] fix: Modify access modes to match YAML 1.2 schema

[eugene-marchanka]

Description of the change

This change updates the access modes to match the YAML 1.2 schema

Benefits

This change is preventing manifests from being malformed due to using YAML autoformatters that comply with the YAML 1.2 schema.

Possible drawbacks

None

Applicable issues

• fixes #

Additional information

Checklist

• [X] Chart version bumped in Chart.yaml according to semver. This is not necessary when the changes only affect README.md files.
• [X] 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)