Fix tab indentation on JumpList.png content entry in WinUIGallery.csproj (#2131)

The `JumpList.png` content entry in `WinUIGallery.csproj` used a tab
character for indentation and was missing the space before `/>`,
inconsistent with surrounding entries that use 4 spaces.

- **`WinUIGallery/WinUIGallery.csproj`**: Replace tab with 4-space
indent and add missing space before `/>` on the `JumpList.png` line

```diff
-	<Content Include="Assets\ControlImages\JumpList.png"/>
+    <Content Include="Assets\ControlImages\JumpList.png" />
```

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