Fix the text color for a navigation callout (elastic#202509)

## Summary

We currently have a problem with the text inside the callout for new
navigation which asks for the feedback.
The PR makes color default so that it correlates with the regular text
color of EUI.
[Slack
conversation](https://elastic.slack.com/archives/C7QC1JV6F/p1733133123930929).


![image](https://github.com/user-attachments/assets/1f6f5e96-1f87-496b-9cc4-3b33beb0efd3)

packages/shared-ux/chrome/navigation/src/ui/components/feedback_btn.tsx

@@ -50,7 +50,7 @@ export const FeedbackBtn: FC<Props> = ({ solutionId }) => {
       onDismiss={onDismiss}
       data-test-subj="sideNavfeedbackCallout"
     >
-      <EuiText size="s" color="dimgrey">
+      <EuiText size="s">
         {i18n.translate('sharedUXPackages.chrome.sideNavigation.feedbackCallout.title', {
           defaultMessage: `How's the navigation working for you? Missing anything?`,
         })}