ci: bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     name: bash -n (syntax)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Syntax-check every shell script
         run: |
           set -e
@@ -30,7 +30,7 @@ jobs:
     name: shellcheck (errors block merge)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Install shellcheck
         run: sudo apt-get update -qq && sudo apt-get install -y shellcheck
       - name: shellcheck --severity=error
@@ -48,7 +48,7 @@ jobs:
     runs-on: ubuntu-latest
     continue-on-error: true
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Install shellcheck
         run: sudo apt-get update -qq && sudo apt-get install -y shellcheck
       - name: shellcheck --severity=warning
@@ -66,7 +66,7 @@ jobs:
     runs-on: ubuntu-latest
     continue-on-error: true
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Install shfmt
         run: |
           curl -fsSL -o /tmp/shfmt \
@@ -86,7 +86,7 @@ jobs:
     name: gitleaks (secret scan)
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - name: gitleaks
@@ -99,7 +99,7 @@ jobs:
     runs-on: ubuntu-latest
     continue-on-error: true
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Check links in README and docs
         uses: gaurav-nelson/github-action-markdown-link-check@v1
         with:

.github/workflows/crs-bump.yml

@@ -14,7 +14,7 @@ jobs:
   bump:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Detect current + latest CRS version
         id: ver