update postgres to run tests on latest node (#3142)

Author: rochdev

.github/workflows/plugins.yml

@@ -733,7 +733,6 @@ jobs:
       # - run: yarn test:plugins:upstream
       - uses: codecov/codecov-action@v2
 
-  # The pg version range we support doesn't work beyond Node 14.
   postgres:
     runs-on: ubuntu-latest
     services:
@@ -753,6 +752,8 @@ jobs:
       - run: yarn install
       - uses: ./.github/actions/node/oldest
       - run: yarn test:plugins:ci
+      - uses: ./.github/actions/node/latest
+      - run: yarn test:plugins:ci
       - uses: codecov/codecov-action@v2
 
   promise: