Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/actionlint.yml

@@ -15,7 +15,7 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Download actionlint
         id: get_actionlint
         run: bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/main/scripts/download-actionlint.bash)

.github/workflows/bashate.yml

@@ -15,7 +15,7 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: 3.14

.github/workflows/checkmake.yml

@@ -14,7 +14,7 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: Uno-Takashi/checkmake-action@v2
         with:
           makefile: _latex/Makefile

.github/workflows/copyrights.yml

@@ -15,7 +15,7 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: yegor256/copyrights-action@0.0.12
         with:
           globs: >-

.github/workflows/deploy.yml

@@ -17,7 +17,7 @@ jobs:
       OPENAI_API_KEY: ${{ secrets.OPENAI_API_KEY }}
       YOUTUBE_API_KEY: ${{ secrets.YOUTUBE_API_KEY }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 3.3 # don't change this
@@ -32,7 +32,7 @@ jobs:
     timeout-minutes: 10
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - run: rm -f Gemfile Gemfile.lock
       - uses: ruby/setup-ruby@v1
         with:
@@ -49,7 +49,7 @@ jobs:
     runs-on: ubuntu-24.04
     needs: [site, icons]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/download-artifact@v6
         with:
           name: site

.github/workflows/eslint.yml

@@ -15,7 +15,7 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - run: npm install -g eslint@9.27.0
       - run: npm install @eslint/js
       - run: eslint --config .github/eslint.config.js

.github/workflows/hadolint.yml

@@ -14,5 +14,5 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: hadolint/hadolint-action@v3.3.0

.github/workflows/jekyll.yml

@@ -15,7 +15,7 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 3.4.7

.github/workflows/markdown-lint.yml

@@ -15,5 +15,5 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: DavidAnson/markdownlint-cli2-action@v21.0.0

.github/workflows/pdd.yml

@@ -15,5 +15,5 @@ jobs:
     timeout-minutes: 15
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: volodya-lombrozo/pdd-action@master