[SYCL][Doc] Update spec template to SYCL rev 11 (#20590)

The SYCL 2020 specification is now at revision 11.

Author: gmlueck

sycl/doc/extensions/template.asciidoc

@@ -37,7 +37,7 @@ https://github.com/intel/llvm/issues
 
 == Dependencies
 
-This extension is written against the SYCL 2020 revision 10 specification.  All
+This extension is written against the SYCL 2020 revision 11 specification.  All
 references below to the "core SYCL specification" or to section numbers in the
 SYCL specification refer to that revision.