[build] Skip CDN assets build when testing docker contexts

[jbudz]

When testing docker contexts we skip all build steps related to Kibana artifacts. CDN assets rely on the Kibana base folder and should be skipped too.

Fixes https://buildkite.com/elastic/kibana-artifacts-snapshot/builds/3445
Build https://buildkite.com/elastic/kibana-artifacts-snapshot/builds/3451
Bug introduced in #169707

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[kibana-ci]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 1f0ae8e

Failed CI Steps

• Investigations - Security Solution Cypress Tests #2
• Defend Workflows Cypress Tests #2

Test Failures

• [job] [logs] Investigations - Security Solution Cypress Tests #2 / Ransomware Detection Alerts Ransomware in Timelines Renders ransomware entries in timelines table Renders ransomware entries in timelines table

Metrics [docs]

✅ unchanged

History

• 💛 Build #173791 was flaky bc54649

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@elasticmachine merge upstream