ci: add npm cache and serialize matrix to reduce 429 errors

Author: ppetzold

.github/workflows/main.yml

@@ -13,6 +13,7 @@ jobs:
         strategy:
             matrix:
                 node-version: [20.x, 22.x]
+            max-parallel: 1
 
         services:
             postgres:
@@ -46,6 +47,7 @@ jobs:
               uses: actions/setup-node@v4
               with:
                   node-version: ${{ matrix.node-version }}
+                  cache: npm
             - run: npm ci
             - run: npm run format:ci
             - run: npm run lint