ci: limit workflow permissions

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

Author: pkuczynski

.github/workflows/tests.yml

@@ -1,5 +1,9 @@
 name: tests
 
+permissions:
+  contents: read
+  pull-requests: write
+
 on:
   push:
     branches: [ master ]