updated actions/checkout to v6 (#603)

Author: firewave

.github/workflows/CI-unixish.yml

@@ -25,7 +25,7 @@ jobs:
       CXX: ${{ matrix.compiler }}
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         persist-credentials: false
 

.github/workflows/CI-windows.yml

@@ -25,7 +25,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
 

.github/workflows/clang-tidy.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-24.04
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
 

.github/workflows/format.yml

@@ -28,7 +28,7 @@ jobs:
       UNCRUSTIFY_INSTALL_DIR: ${{ github.workspace }}/runformat-uncrustify
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false