Remove unterminated "::group::" in final echo

The debug output job had an echo to start a group, but never terminated
it. Let's just remove the whole thing.

Author: mhucka

.github/workflows/ci.yaml

@@ -625,4 +625,3 @@ jobs:
           echo '::group:: GitHub runner context'
           echo "$RUNNER_CONTEXT"
           echo '::endgroup::'
-          echo '::group:: Matrix context'