make artifact name unique

Author: Victor Tang

.github/workflows/target_tests.yml

@@ -71,5 +71,5 @@ jobs:
         if: ${{ always() }}
         uses: actions/upload-artifact@v4
         with:
-          name: code-coverage-report
+          name: code-coverage-report-${{ matrix.target.MBED_TARGET }}
           path: ${{ env.JUNIT_OUTPUT }}