Update actions/checkout to version 4 (#224)

Author: Jacob Lamb

README.md

@@ -28,7 +28,7 @@ jobs:
   linkChecker:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Link Checker
         id: lychee
@@ -65,7 +65,7 @@ jobs:
   linkChecker:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Link Checker
         uses: lycheeverse/[email protected]