ci: fix cache key mismatch in test job

Change cache restore key from 'ubuntu-latest' to 'Linux' to match the
build job's save key. The build job uses ${{ runner.os }} which evaluates
to 'Linux' on ubuntu-latest, not 'ubuntu-latest'.

This resolves the "Failed to restore cache entry" error.

Author: jdalton

.github/workflows/ci.yml

@@ -110,7 +110,7 @@ jobs:
           path: |
             dist
             node_modules
-          key: build-${{ github.sha }}-ubuntu-latest
+          key: build-${{ github.sha }}-Linux
           fail-on-cache-miss: true
 
       - name: Install dependencies (Windows)