Skip mathlib cache retrieval when .lake cache restored

[Copilot]

CI was retrieving mathlib cache unconditionally, even when .lake was successfully restored from cache (which already contains mathlib).

Changes

• Added conditional to skip lake exe cache get when cache-restore step hits cache

- name: Get Mathlib cache
  if: steps.cache-restore.outputs.cache-hit != 'true'
  run: lake exe cache get

Reduces CI time on cache hits while preserving behavior on cache misses.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.