build(deps): 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] <[email protected]>

Author: dependabot[bot]

.github/workflows/macos-linux-windows-pixi.yml

@@ -51,7 +51,7 @@ jobs:
             environment: clang-cl
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           submodules: recursive
 
@@ -93,7 +93,7 @@ jobs:
         os: [ubuntu-latest, macos-latest, macos-15-intel, windows-latest]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           submodules: recursive
 

.github/workflows/update_pixi_lockfile.yml

@@ -19,7 +19,7 @@ jobs:
           app-id: ${{ secrets.APP_ID }}
           private-key: ${{ secrets.APP_PRIVATE_KEY }}
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           token: ${{ steps.generate-token.outputs.token }}
           ref: devel