fix CI cache and test node 16

Author: MartijnR

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version:   ['18.18.0', '20.5.1']
+        node-version:   ['16.20.2', '18.18.2', '20.5.1']
     steps:
       - uses: actions/checkout@v3
       - uses: volta-cli/action@v4
@@ -22,7 +22,7 @@ jobs:
         id: cache
         with:
           path: node_modules
-          key: ${{ matrix.node }}-${{ hashFiles('**/yarn.lock') }}
+          key: ${{ matrix.node-version }}-${{ hashFiles('**/yarn.lock') }}
       - if: steps.cache.outputs.cache-hit != 'true'
         run: yarn install
       - run: yarn test