[SYCL] Pass OCL_ICD_VENDORS to LIT (#16133)

Tests can fail if `OCL_ICD_VENDORS` is needed but not set.

Author: Hugh Delaney

sycl/test-e2e/lit.cfg.py

@@ -75,6 +75,7 @@
     [
         "PATH",
         "OCL_ICD_FILENAMES",
+        "OCL_ICD_VENDORS",
         "CL_CONFIG_DEVICES",
         "SYCL_DEVICE_ALLOWLIST",
         "SYCL_CONFIG_FILE_NAME",