Bump node version from 16 to 20, also bump checkout action version to resolve node deprecations (#11)

* Bump node version from 16 to 20, also bump checkout action version to resolve node deprecations

* revert test changes to ensure we're testing with the latest dhall version

Author: learoyklinginsmith

.github/workflows/main.yml

@@ -15,7 +15,7 @@ jobs:
           - 1.34.0
           - latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Setup Dhall
         uses: ./

action.yml

@@ -15,5 +15,5 @@ inputs:
     required: false
 
 runs:
-  using: node16
+  using: node20
   main: src/action.js