ci(coverage): fix ReportGenerator action ref

The action repo is danielpalme/ReportGenerator-GitHub-Action (hyphenated)
and its tags are v-prefixed. Pin to @v5.5.10.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: marius-bughiu

.github/workflows/coverage.yml

@@ -53,7 +53,7 @@ jobs:
           --results-directory ./TestResults/coverage
 
       - name: Generate report
-        uses: danielpalme/ReportGenerator-GitHubAction@5.5.10
+        uses: danielpalme/ReportGenerator-GitHub-Action@v5.5.10
         with:
           reports: 'src/TestResults/coverage/**/coverage.cobertura.xml'
           targetdir: 'coveragereport'