chore: update gh actions

I noticed GH actions is failing because it's building on node 14 and 16.

These are pretty out of date so update to use LTS (20) and Current (21).

.github/workflows/main.yml

@@ -1,22 +1,29 @@
 name: CI
-on: [push]
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
 jobs:
   build:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: ['14', '16']
+        node: ['lts/*', 'current']
     steps:
       - name: Begin CI...
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Use Node ${{ matrix.node }}
-        uses: actions/setup-node@v1
+        uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node }}
 
       - name: Use cached node_modules
-        uses: actions/cache@v1
+        uses: actions/cache@v4
         with:
           path: node_modules
           key: nodeModules-${{ hashFiles('**/package-lock.json') }}-${{ matrix.node }}