Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/cleanup.yml

@@ -27,7 +27,7 @@ jobs:
     runs-on: ubuntu-latest
     #gt-placeholder-runs-on-end
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       #gt-placeholder-install-dependencies-start
       #gt-placeholder-install-dependencies-end

.github/workflows/gt-update.yml

@@ -66,7 +66,7 @@ jobs:
           	} && false || cd "$currentDir" && rm -r "$tmpDir" && "${result:-false}"
           # end install.doc.sh
       #gt-placeholder-gh-action-checkout-1-start
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       #gt-placeholder-gh-action-checkout-1-end
       - id: set-matrix
         run: |
@@ -114,7 +114,7 @@ jobs:
           	} && false || cd "$currentDir" && rm -r "$tmpDir" && "${result:-false}"
           # end install.doc.sh
       #gt-placeholder-gh-action-checkout-2-start
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       #gt-placeholder-gh-action-checkout-2-end
       - name: reset gpg keys
         run: gt reset --gpg-only true -r "${{ matrix.remote }}"
@@ -163,7 +163,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       #gt-placeholder-gh-action-checkout-3-start
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       #gt-placeholder-gh-action-checkout-3-end
       - name: check if signing key already are or will expire within the next 3 months
         run: |

.github/workflows/quality-assurance.yml

@@ -15,7 +15,7 @@ jobs:
     name: before-pr.sh
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Setup JDK 17
         uses: actions/setup-java@v5
         with:
@@ -34,7 +34,7 @@ jobs:
     outputs:
       matrix: ${{ steps.set-matrix.outputs.matrix }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 1
       - id: set-matrix
@@ -51,7 +51,7 @@ jobs:
     env:
       JAVA_VERSION: ${{ matrix.java_version }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: "Set up JDK ${{ matrix.java_version }}"
         uses: actions/setup-java@v5
         with: