Bump actions/download-artifact from 4 to 6

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

---
updated-dependencies:
- dependency-name: actions/download-artifact
  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/codeql_unit_tests.yml

@@ -171,7 +171,7 @@ jobs:
           script: |
             core.setFailed('Test run job failed')
       - name: Collect test results
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
 
       - name: Validate test results
         run: |

.github/workflows/standard_library_upgrade_tests.yml

@@ -162,7 +162,7 @@ jobs:
           python-version: "3.9"
 
       - name: Collect test results
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v6
 
       - name: Validate test results
         shell: python