[WIP][CI] Backward-compatibility testing against sycl-rel-6_3

Author: aelovikov-intel

.github/workflows/sycl-linux-run-tests.yml

@@ -159,6 +159,7 @@ on:
         options:
           - 'ghcr.io/intel/llvm/sycl_ubuntu2404_nightly:latest'
           - 'ghcr.io/intel/llvm/sycl_prebuilt_tests:sycl-rel-6_2'
+          - 'ghcr.io/intel/llvm/sycl_prebuilt_tests:sycl-rel-6_3'
           - 'ghcr.io/intel/llvm/ubuntu2404_intel_drivers:alldeps'
       image_options:
         description: |