Bump the gh-action-workflows group with 2 updates

Bumps the gh-action-workflows group with 2 updates: [actions/checkout](https://github.com/actions/checkout) and [actions/upload-artifact](https://github.com/actions/upload-artifact).


Updates `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)

Updates `actions/upload-artifact` from 4 to 6
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: gh-action-workflows
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: gh-action-workflows
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/R-CMD-check-cross.yaml

@@ -25,7 +25,7 @@ jobs:
       R_KEEP_PKG_SOURCE: yes
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
 
@@ -59,7 +59,7 @@ jobs:
             Rscript -e 'rcmdcheck::rcmdcheck("/root/work/QuickJSR/QuickJSR", args = c("--no-manual", "--as-cran"), check_dir = "/root/work/QuickJSR/QuickJSR/check")'
 
       - name: Upload check results
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         with:
           name: arch-${{ matrix.config.platform }}-results
           path: check

.github/workflows/R-CMD-check.yaml

@@ -44,7 +44,7 @@ jobs:
       MAKEFLAGS: -j4
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true
 

.github/workflows/test-rstan.yaml

@@ -29,7 +29,7 @@ jobs:
       MAKEFLAGS: -j4
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           submodules: true