[material-ui] Fix slots typing for Tooltip and StepLabel

[siriwatknp]

closes #44637

Root cause

The previous slots types is too narrow

export interface StepLabelSlots {
  /**
   * The component to render in place of the [`StepIcon`](https://mui.com/material-ui/api/step-icon/).
   */
  stepIcon: React.ElementType<StepIconProps>;
}

It's specific to StepIconProps, meaning using plain HTML like "div" or a custom component won't work.

<StepLabel
  slots={{
    stepIcon: 'div', // ❌ type error
  }}
>
  Step One
</StepLabel>;

Fix

Widening the types to just React.ElementType to include plain HTML and any custom React component.

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[mui-bot]

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[aarongarciah]

@siriwatknp I think you wanted to link this issue in the PR description #44952