Fix Kotlin file icon extraction

What does this MR do?

Fix Kotlin file icon extraction

It seems that JetBrains changed the structure of their Kotlin brand assets zip file.

The old "Digital/Mark/One Color/Kotlin One Color Logo Mark RGB.svg" file no longer exists in the archive, as of 2025-10-29.

We now use "Kotlin Ecosystem Logos/Kotlin/Primary/Kotlin icon.svg", which is a full colour version of the logo, because:

• Their guidelines say "The full-color version is the main one and should be used in the vast majority of cases."
• Most of our other file icons are colourful.
• The original reason for using a single colour version seems to have been due to some kind of SVG optimisation issue, which doesn't seem to be relevant any more.

Finally, it's worth noting that this upstream change broke our pipelines, since the build script checks that the Kotlin file icon exists.

This commit doesn't protect us against future breakages; we probably need a more robust solution for long term safety.

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