💥 Drop Node.js 14 and add Node.js 20

According to the Node.js [release schedule][1]:

 - v14 will be end-of-lifed on 30 April
 - v20 has been released

This change drops v14 from our test matrix, and adds v20.

[1]: https://nodejs.dev/en/about/releases/

.github/workflows/test.yml

@@ -15,9 +15,9 @@ jobs:
     strategy:
       matrix:
         node:
-        - 14
         - 16
         - 18
+        - 20
     services:
       mongodb:
         image: mongo:4.4