[Infrastructure] Bump actions/checkout from 5 to 6 (AliceO2Group#13944)

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/mega-linter.yml

@@ -23,7 +23,7 @@ jobs:
     steps:
       # Git Checkout
       - name: Checkout Code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           # Checkout the HEAD of the PR instead of the merge commit.
           ref: ${{ github.event.pull_request.head.sha }}

.github/workflows/o2-linter.yml

@@ -30,7 +30,7 @@ jobs:
           echo BRANCH_HEAD="$branch_head" >> "$GITHUB_ENV"
           echo BRANCH_BASE="$branch_base" >> "$GITHUB_ENV"
       - name: Checkout Code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ env.BRANCH_HEAD }}
           fetch-depth: 0 # needed to get the full history