runner: Use larger pixmap

This avoids a low quality icon being visible as a search result when searching in the application launcher.

Before (5.25):

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Before (master):

After (master+MR):

Because the application launcher was recently changed to have larger icons, this is now more visible.

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There is a drawback - applications with different icons for different sizes will always use the larger icon. This is already visible in master, because of the icon size change in the launcher - it uses the wrong, smaller icon. The fix also makes it use the correct icon, however, krunner will use the wrong, larger icon (but it will be downscaled, not upscaled).

And in krunner:

Before (master/5.25):

After (master+mr):