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

@@ -43,7 +43,7 @@ jobs:
         ports:
           - 5432:5432
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       if: github.event.action == 'opened' || github.event.action == 'synchronize' || github.event.ref == 'refs/heads/main'
 
     - name: "Configure ghcup"

.github/workflows/linting.yml

@@ -9,7 +9,7 @@ jobs:
   fourmolu:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - uses: haskell-actions/run-fourmolu@v11
       with:
@@ -21,7 +21,7 @@ jobs:
   hlint:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: 'Set up HLint'
       uses: haskell-actions/hlint-setup@v2