CI: bump unit test actions

The code coverage no longer works on Node.js 8 due to a (transitive)
dependency of nyc made a breaking change. Luckily Node.js 8 is
already covered by the integration tests so the easiest option is to
remove it from the unit tests.

Author: lovell

.github/workflows/unit.yml

@@ -9,7 +9,6 @@ jobs:
     strategy:
       matrix:
         node-version:
-          - 8
           - 10
           - 12
           - 14
@@ -18,9 +17,9 @@ jobs:
           - 20
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Install Node.js
-        uses: actions/setup-node@v3
+        uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node-version }}
       - name: Install dependencies