ci: bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...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

@@ -27,7 +27,7 @@ jobs:
             install-rg: choco install ripgrep
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: rhysd/action-setup-vim@v1
         with:

.github/workflows/docgen.yml

@@ -17,7 +17,7 @@ jobs:
           - os: ubuntu-latest
             url: https://github.com/neovim/neovim/releases/download/v0.9.5/nvim-linux64.tar.gz
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - run: date +%F > todays-date
       - name: Restore cache for today's nightly.
         uses: actions/cache@v4

.github/workflows/lint.yml

@@ -14,7 +14,7 @@ jobs:
     name: Luacheck
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Prepare
         run: |
@@ -29,7 +29,7 @@ jobs:
     name: stylua
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: JohnnyMorganz/stylua-action@v4
         with:
           token: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/release.yml

@@ -9,7 +9,7 @@ jobs:
   luarocks-upload:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: LuaRocks Upload
         uses: lumen-oss/luarocks-tag-release@v7
         env: