Fix last SonarCloud security hotspot: dependency-check SHA

Use full SHA for dependency-check/Dependency-Check_Action instead of
branch reference "main" to satisfy supply chain security requirements.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: reidspencer

.github/workflows/scala.yml

@@ -170,7 +170,7 @@ jobs:
       uses: actions/checkout@v4
 
     - name: Run Dependency Check
-      uses: dependency-check/Dependency-Check_Action@main
+      uses: dependency-check/Dependency-Check_Action@1e54355a8b4c8abaa8cc7d0b70aa655a3bb15a6c # main
       with:
         project: 'riddl'
         path: '.'