build(deps): bump actions/upload-artifact from 5 to 6

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v5...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] <support@github.com>

.github/workflows/tests.yml

@@ -45,7 +45,7 @@ jobs:
         if: github.event_name == 'pull_request' && matrix.go == 'stable'
 
       - name: Upload artifact with ShellCheck defects in SARIF format
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: Differential ShellCheck SARIF
           path: ${{ steps.ShellCheck.outputs.sarif }}
@@ -559,7 +559,7 @@ jobs:
 
       - name: Upload incus client artifacts
         if: matrix.go == 'stable'
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         continue-on-error: true
         with:
           name: ${{ runner.os }}
@@ -608,7 +608,7 @@ jobs:
 
       - name: Upload documentation artifacts
         if: always()
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: documentation
           path: doc/html