Potential fix for code scanning alert no. 80: Workflow does not contain permissions

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: JesperDramsch

.github/workflows/link-check.yml

@@ -9,6 +9,10 @@ on:
     paths:
       - '_data/conferences.yml'
 
+permissions:
+  contents: read
+  issues: write
+
 jobs:
   check-links:
     runs-on: ubuntu-latest