CTS issue workflow: Don't assign PR author to issue

The workflow may fail when trying to assign a person that is not a
member of the @KhronosGroup organization to the CTS issue.
Unfortunately there is no simple way of detecting this in advance, so we
instead remove the assignment mechanism altogether.

.github/workflows/open_cts_issue.yml

@@ -31,8 +31,6 @@ jobs:
           repo: SYCL-CTS
           title: |
             [Spec change] ${{ github.event.pull_request.title }}
-          # Assign person who opened PR
-          assignees: ${{ github.triggering_actor }}
           body: |
             Please review whether ${{ github.event.pull_request.html_url }} by @${{ github.triggering_actor }} requires any changes to the CTS.