[Alerting][UI] Fixes missing EUI theme in context

[claudiopro]

Summary

This PR addresses a missing EUI theme in the context of the Triggers Actions UI component tree, resulting in an error when rendering the chart preview for some rule types.

Fixes #121793.

Checklist

• Unit or functional tests were updated or added to match the most common scenarios
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)
• This was checked for cross-browser compatibility

[claudiopro]

Regression from #121415.

[claudiopro]

See #121415 (comment) for an explanation.

[claudiopro]

This is not an issue in v8.0, as the change #121415 was only merged in main.

[ymao1]

Thanks for fixing! LGTM

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 39e2830
• Storybooks Preview

Metrics [docs]

Module Count

Fewer modules leads to a faster build time

id	before	after	diff
triggersActionsUi	330	332	+2

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
triggersActionsUi	780.3KB	780.9KB	+578.0B

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
triggersActionsUi	53.8KB	53.9KB	+49.0B

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[kibanamachine]

💔 Backport failed

The backport operation could not be completed due to the following error:
There are no branches to backport to. Aborting.

The backport PRs will be merged automatically after passing CI.

To backport manually run:
node scripts/backport --pr 121796