Use checkout v4 so we don't get the deprecation warnings (#126)

Author: tbttfox

.github/workflows/main.yml

@@ -37,7 +37,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           submodules: true
 
@@ -89,7 +89,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           submodules: true
 
@@ -141,7 +141,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           submodules: true