limit parallel tests to avoid rate limits

Author: josiasmontag

.github/workflows/run-tests.yml

@@ -14,6 +14,7 @@ jobs:
         runs-on: ubuntu-latest
 
         strategy:
+            max-parallel: 2
             matrix:
                 node-version: [20, 22, 23]
                 # See supported Node.js release schedule at https://nodejs.org/en/about/releases/