[UR] Use reference counting on factories

Pre-commit MR for oneapi-src/unified-runtime#2048

Author: RossBrunton

sycl/cmake/modules/FetchUnifiedRuntime.cmake

@@ -117,13 +117,11 @@ if(SYCL_UR_USE_FETCH_CONTENT)
   endfunction()
 
   set(UNIFIED_RUNTIME_REPO "https://github.com/oneapi-src/unified-runtime.git")
-  # commit b766009add8dc41ad03e2a63be9f6ed40eea4c55 (HEAD, origin/main, origin/HEAD)
-  # Merge: 608e9184 c3c57284
-  # Author: Omar Ahmed <omar.ahmed@codeplay.com>
-  # Date:   Tue Aug 27 16:30:04 2024 +0100
-  #   Merge pull request #2011 from nrspruit/fix_opencl_usm_align_check
-  #   [OpenCL] Fix USM alignment error check to occur always and return nulllptr
-  set(UNIFIED_RUNTIME_TAG b766009add8dc41ad03e2a63be9f6ed40eea4c55)
+  # commit put-commit-here
+  # Author: Ross Brunton <ross@codeplay.com>
+  # Date:   Wed Sep 4 17:25:11 2024 +0100
+  # Use reference counting on factories
+  set(UNIFIED_RUNTIME_TAG 6898550fcf13cc59365e28cf36d96334d21a4d5c)
 
   set(UMF_BUILD_EXAMPLES OFF CACHE INTERNAL "EXAMPLES")
   # Due to the use of dependentloadflag and no installer for UMF and hwloc we need