fix: remove unused coverage reporting step from GQM workflow

The GQM update workflow only generates a Mermaid diagram and never
produces NYC coverage output, so the coverage reporting step always
failed with a missing file error.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jeffabailey

.github/workflows/gqm_update.yml

@@ -37,8 +37,3 @@ jobs:
           cd scripts/gqm_gen
           ./update_gqm.sh
 
-      - name: Report coverage
-        if: success()
-        uses: sidx1024/report-nyc-coverage-github-action@v1.2.7
-        with:
-          coverage_file: ".nyc_output/nyc-coverage-report/coverage-summary.json"