Remove Node 18 from the CI build

Author: sbates-idrc

.github/workflows/ci.yaml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-22.04]
-        node-version: [18.x, 20.x]
+        node-version: [20.x]
     runs-on: ${{ matrix.os }}
     env:
       CI: true