Update actions/checkout to v4

v3 uses Node 16 which is deprecated

Author: dmadison

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Setup Arduino CLI
         uses: arduino/setup-arduino-cli@v1.1.2

.github/workflows/docs.yml

@@ -9,7 +9,7 @@ jobs:
   docs:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Fetch Repository Reference Info
         id: repo-info
         run: |