ci: reset npm cache before windows global install

Author: mldangelo

.github/workflows/test.yml

@@ -79,6 +79,12 @@ jobs:
         with:
           node-version: "24"
 
+      - name: Configure npm cache on Windows
+        if: matrix.os == 'windows-latest'
+        run: |
+          "NPM_CONFIG_CACHE=$env:RUNNER_TEMP\\npm-cache" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+          npm cache clean --force
+
       - name: Install promptfoo globally
         run: npm install -g promptfoo@latest
         env: