IconImageSource not appearing for secondary ToolbarItems on Android and Catalyst

### Description

After the implementation of secondary toolbar support for iOS and Mac Catalyst in https://github.com/dotnet/maui/pull/28185 the IconImageSource property does not render for secondary toolbar items on Android and Mac Catalyst.

| Expected Output | Actual Output |
|-----------------|---------------|
| | |

Expected Behavior
IconImageSource should be rendered for both primary and secondary toolbar items across all platforms, including Android and Catalyst.

### Steps to Reproduce

### Link to public reproduction project repository

[src/Controls/samples/Controls.Sample/Pages/Core/ToolbarPage.xaml](https://github.com/dotnet/maui/blob/459675e046c5ac00742c592c3f9284d2524c4775/src/Controls/samples/Controls.Sample/Pages/Core/ToolbarPage.xaml)
### Version with bug

10.0.0-preview.6

### Is this a regression from previous behavior?

Not sure, did not test other versions

### Last version that worked well

_No response_

### Affected platforms

Android, macOS

### Affected platform versions

_No response_

### Did you find any workaround?

_No response_

### Relevant log output

```shell

```