Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/build.yaml

@@ -13,7 +13,7 @@ jobs:
       matrix:
         os: [ ubuntu-20.04, ubuntu-22.04, ubuntu-24.04 ]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: "Update dependencies"
         run: sudo apt-get update
       - name: "Install dependencies"
@@ -29,7 +29,7 @@ jobs:
       matrix:
         os: [ macos-13, macos-14 ]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: "Install dependencies"
         run: brew tap robotology/formulae && brew install cmake pkg-config qt@5
       - name: "Build"