Add issue write permissions to mutants cron job workflow

Our current workflow permisssions do not allow for writing issues
but I had made a workflow that already had this in place so we just
had a failed workflow that did not properly create the issue as
expected.

Author: benalleng

.github/workflows/cron-weekly-mutants.yml

@@ -6,6 +6,8 @@ on:
 jobs:
   cargo-mutants:
     runs-on: ubuntu-latest
+    permissions:
+      issues: write
     steps:
       - uses: actions/checkout@v4
       - uses: taiki-e/install-action@v2