Updated checkout action version.

Author: akb825

.github/workflows/main.yml

@@ -29,7 +29,7 @@ jobs:
           cmake_args: "-DVFC_SHARED=ON"
     steps:
     - name: checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Download submodules
       run: git submodule update --init
       working-directory: "${{ github.workspace }}"
@@ -94,7 +94,7 @@ jobs:
           cmake_args: "-DVFC_SHARED=ON"
     steps:
     - name: checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Download submodules
       run: git submodule update --init
       working-directory: "${{ github.workspace }}"
@@ -167,7 +167,7 @@ jobs:
           cmake_args: "-DVFC_SHARED=ON"
     steps:
     - name: checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Download submodules
       run: git submodule update --init
       shell: bash