[Discover] Fix styles typo (#225339)

## Summary

Quick fix with styles typo, according to [this
comment](https://github.com/elastic/kibana/pull/224586#discussion_r2166795813).
I had auto merge on in [[Discover] Align SCSS - Emotion migration part 2
with new guidelines](https://github.com/elastic/kibana/pull/224586#top)
and accidentally got merged with typo.


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [ ] If a plugin configuration key changed, check if it needs to be
allowlisted in the cloud and added to the [docker
list](https://github.com/elastic/kibana/blob/main/src/dev/build/tasks/os_packages/docker_generator/resources/base/bin/kibana-docker)
- [ ] This was checked for breaking HTTP API changes, and any breaking
changes have been approved by the breaking-change committee. The
`release_note:breaking` label should be applied in these situations.
- [ ] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed
- [ ] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

### Identify risks

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to test bugs, performance regression, potential of data loss.

Describe the risk, its severity, and mitigation for each identified
risk. Invite stakeholders and evaluate how to proceed before merging.

- [ ] [See some risk
examples](https://github.com/elastic/kibana/blob/main/RISK_MATRIX.mdx)
- [ ] ...

src/platform/plugins/shared/discover/public/application/main/components/layout/discover_layout.tsx

@@ -374,7 +374,7 @@ export function DiscoverLayout({ stateContainer }: DiscoverLayoutProps) {
       data-fetch-counter={fetchCounter.current}
       direction="column"
       css={[
-        styles.DscPage,
+        styles.dscPage,
         css`
           ${useEuiBreakpoint(['m', 'l', 'xl'])} {
             ${kbnFullBodyHeightCss(TABS_ENABLED ? '32px' : undefined)}