chore: update devcontainers icon (#850)

Updates the devcontainers icon to use the [Microsoft Fluent UI
`ic_fluent_cube_32_filled`](78c9587b99/assets/Cube/SVG/ic_fluent_cube_32_filled.svg),
consistent with
[coder/coder#24478](https://github.com/coder/coder/pull/24478).

> 🤖 This PR was created with the help of Coder Agents, and needs a human
review. 🧑💻

.icons/devcontainers.svg

@@ -1 +1,3 @@
-<svg xmlns="http://www.w3.org/2000/svg" width="800" height="800" viewBox="0 0 32 32"><title>file_type_devcontainer</title><circle cx="16" cy="16" r="14" style="fill:#193e63"/><polygon points="10.777 22.742 9.343 21.348 12.729 17.865 9.346 14.417 10.774 13.017 15.525 17.859 10.777 22.742" style="fill:#add1ea"/><polygon points="21.42 19.101 22.854 17.706 19.468 14.224 22.851 10.776 21.423 9.376 16.672 14.218 21.42 19.101" style="fill:#add1ea"/></svg>
+<svg width="32" height="32" viewBox="0 0 32 32" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M13.8461 2.7571C15.2325 2.22387 16.7675 2.22387 18.1539 2.7571L28.0769 6.57367C29.2355 7.01927 30 8.13239 30 9.3737V22.6265C30 23.8678 29.2355 24.9809 28.0769 25.4265L18.1539 29.2431C16.7675 29.7763 15.2325 29.7763 13.8461 29.2431L3.92306 25.4265C2.76449 24.9809 2 23.8678 2 22.6265V9.3737C2 8.13239 2.76449 7.01927 3.92306 6.57367L13.8461 2.7571ZM9.39418 10.0809C8.88655 9.86331 8.29867 10.0985 8.08111 10.6061C7.86356 11.1137 8.09871 11.7016 8.60634 11.9192L15.0003 14.6594V21C15.0003 21.5523 15.448 22 16.0003 22C16.5525 22 17.0003 21.5523 17.0003 21V14.6594L23.3942 11.9192C23.9018 11.7016 24.137 11.1137 23.9194 10.6061C23.7018 10.0985 23.114 9.86331 22.6063 10.0809L16.0003 12.912L9.39418 10.0809Z" fill="#212121"/>
+</svg>