[SYCL][Doc] Update spec template (#12283)

Update the template for extension specifications to list the new
copyright date and the most current core SYCL revision.

Author: gmlueck

sycl/doc/extensions/template.asciidoc

@@ -20,7 +20,7 @@
 == Notice
 
 [%hardbreaks]
-Copyright (C) 2023-2023 Intel Corporation.  All rights reserved.
+Copyright (C) 2024-2024 Intel Corporation.  All rights reserved.
 
 Khronos(R) is a registered trademark and SYCL(TM) and SPIR(TM) are trademarks
 of The Khronos Group Inc.  OpenCL(TM) is a trademark of Apple Inc. used by
@@ -36,7 +36,7 @@ https://github.com/intel/llvm/issues
 
 == Dependencies
 
-This extension is written against the SYCL 2020 revision 7 specification.  All
+This extension is written against the SYCL 2020 revision 8 specification.  All
 references below to the "core SYCL specification" or to section numbers in the
 SYCL specification refer to that revision.