build(deps): bump actions/upload-artifact from 4 to 6

Bumps [actions/upload-artifact](https://github.com/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/upload-artifact
  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/linux.yml

@@ -91,7 +91,7 @@ jobs:
           LC_ALL=fr_FR.UTF-8 meson test -C build --print-errorlogs --setup=valgrind \
                                                  --no-suite python-tests
       - name: Upload test logs
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         if: failure()
         with:
           name: test logs
@@ -106,7 +106,7 @@ jobs:
                 exit 1
             fi
       - name: Store doxygen docs for use by the pages workflow
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v6
         if: success() && matrix.compiler == 'gcc' && matrix.sanitizers == 'sanitizers'
         with:
           name: doxygen-docs