fix: Export path for internal testing utilities (#82)

Author: fralongo

package.json

@@ -14,7 +14,7 @@
     ".": "./index.js",
     "./dom": "./dom/index.js",
     "./internal": "./internal/index.js",
-    "./internal/testing": "./internal/testing/index.js",
+    "./internal/testing": "./internal/testing.js",
     "./internal/analytics-metadata": "./internal/analytics-metadata/index.js",
     "./internal/analytics-metadata/utils": "./internal/analytics-metadata/utils.js",
     "./package.json": "./package.json"