Bump test image versions

Description

Updates default versions of testing images to latest patched versions.

Checklist

[x] Chart version bumped in Chart.yaml
[x] Any new variables have documentation and examples in values.yaml, even if commented out
[x] Any new variables added to the README.md
[x] Squash into a single commit (or explain why you'd prefer not to), except...
[x] ...additional commit added for CHANGELOG.md entry
[x] Helm lint + tests passing?

gocd / helm-chart