Bump actions/checkout to v4

Author: Tinche

.github/workflows/main.yml

@@ -18,7 +18,7 @@ jobs:
       fail-fast: false
 
     steps:
-      - uses: "actions/checkout@v3"
+      - uses: "actions/checkout@v4"
 
       - uses: "actions/setup-python@v5"
         with:
@@ -45,7 +45,7 @@ jobs:
     runs-on: "ubuntu-latest"
 
     steps:
-      - uses: "actions/checkout@v3"
+      - uses: "actions/checkout@v4"
 
       - uses: "actions/setup-python@v5"
         with:
@@ -99,7 +99,7 @@ jobs:
     runs-on: "ubuntu-latest"
 
     steps:
-      - uses: "actions/checkout@v3"
+      - uses: "actions/checkout@v4"
       - uses: "actions/setup-python@v5"
         with:
           python-version: "3.12"