Add SYCL 2020 (Revision 10) to issue templates

We should have done this when Revision 10 was released, but missed it.

I left Revision 9 in place because there is a non-zero chance a reporter will
be looking at a stale copy. This will give us a quick way to identify issues
that may be stale for triage.

Author: Pennycook

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -16,6 +16,7 @@ body:
       description: |
         What version of the specification contains the bug?
       options:
+        - SYCL 2020 (Revision 10)
         - SYCL 2020 (Revision 9)
         - SYCL 2020 (Source)
         - SYCL Next (Source)

.github/ISSUE_TEMPLATE/clarification_request.yml

@@ -14,6 +14,7 @@ body:
       description: |
         What version of the specification is unclear?
       options:
+        - SYCL 2020 (Revision 10)
         - SYCL 2020 (Revision 9)
         - SYCL 2020 (Source)
         - SYCL Next (Source)