Update test git ref to upstream/master

Author: adrianfish

webcomponents/tool/src/main/frontend/package.json

@@ -11,7 +11,7 @@
     "bundle": "esbuild \"bundle-entry-points/*.js\" --sourcemap --preserve-symlinks --bundle --splitting --format=esm --outdir=bundles --minify",
     "analyze-bundle": "esbuild \"bundle-entry-points/*.js\" --preserve-symlinks --splitting --bundle --metafile=meta.json --format=esm --outdir=bundles --minify",
     "analyze": "lit-analyzer --strict --quiet --rules.no-complex-attribute-binding=warning --rules.no-incompatible-type-binding=off \"packages/**/src/*.js\"",
-    "test": "lerna run test --concurrency 1 --since HEAD~1 --stream",
+    "test": "lerna run test --concurrency 1 --since upstream/master --stream",
     "test-diff": "lerna run test --concurrency 1 --since HEAD --stream"
   },
   "keywords": [],