GA(deps): 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

@@ -17,7 +17,7 @@ jobs:
         ghc: ["9.12.2"]
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: haskell-actions/setup@v2
       name: Setup Haskell
@@ -43,7 +43,7 @@ jobs:
         cabal: ["3.14"]
         ghc: ["9.12.2"]
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: haskell-actions/setup@v2
       name: Setup Haskell
@@ -78,7 +78,7 @@ jobs:
         cabal: ["3.14"]
         ghc: ["9.12.2"]
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: haskell-actions/setup@v2
       name: Setup Haskell
@@ -113,7 +113,7 @@ jobs:
         cabal: ["3.14"]
         ghc: ["9.12.2"]
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: haskell-actions/setup@v2
       name: Setup Haskell
@@ -139,7 +139,7 @@ jobs:
         cabal: ["3.14"]
         ghc: ["9.12.2"]
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: haskell-actions/setup@v2
       name: Setup Haskell