ci: remove node 19 (#1883)

## Describe your changes

Node 19 has reached end of life a long time ago. It's more recommended
to test [LTS](https://nodejs.org/en/about/previous-releases) instead of
intermediate version.
NB: Node 18 has entered it's maintenance phase in october, and Node 20
is now recommended. I think it would be great to upgrade for all the new
features and perf gain.

- Use Node20 instead of Node19 in test matrix

.github/workflows/tests.yaml

@@ -16,7 +16,7 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             matrix:
-                node-version: [18.x, 19.x]
+                node-version: [18.x, 20.x]
 
         steps:
             - uses: actions/checkout@v3