Update to node 20

As suggested by github:

https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

src/actions/ghci-osbuild/action.yml

@@ -47,5 +47,5 @@ inputs:
       This uses `github.token` by default.
     default: ${{ github.token }}
 runs:
-  using: 'node16'
+  using: 'node20'
   main: 'index.js'

src/actions/netwait/action.yml

@@ -27,5 +27,5 @@ inputs:
       This uses `16` by default.
     default: 16
 runs:
-  using: 'node16'
+  using: 'node20'
   main: 'index.js'

src/actions/privdocker/action.yml

@@ -26,5 +26,5 @@ inputs:
       This prints "Nothing to do." by default.
     default: 'echo "Nothing to do."'
 runs:
-  using: 'node16'
+  using: 'node20'
   main: 'index.js'