ci: skip bun cache restore when node_modules hits

The bun install cache (~470MB, ~104k files) only benefits 'bun install'
runs. When node_modules cache hits, we skip install entirely, so
restoring the bun cache wastes ~37 seconds extracting files we never use.

Add condition to only restore bun cache on node_modules miss.

Author: ammar-agent

.github/actions/setup-mux/action.yml

@@ -23,6 +23,7 @@ runs:
           ${{ runner.os }}-${{ runner.arch }}-bun-${{ steps.bun-version.outputs.version }}-node-modules-
 
     - name: Cache bun install cache
+      if: steps.cache-node-modules.outputs.cache-hit != 'true'
       id: cache-bun-install
       uses: actions/cache@v4
       with: