Nightly: Add job-level permissions to style

[saimanikant]

Description

Nightly is failing due to recent changes:
https://github.com/ansys/pyhps/actions/runs/27321144681

nightly.yml has top-level permissions: {}, which means every job starts with contents: none.
Your reusable workflow style.yml contains jobs style and doc-style that require contents: read, so GitHub rejects the call unless the caller job grants it.

This PR fixes the issue:
https://github.com/ansys/pyhps/actions/runs/27355995606

Checklist

• I have tested these changes locally.
• I have added unit tests (if appropriate).
• I have added necessary documentation or updated existing documentation.
• I have linked the issue(s) addressed by this PR if any.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.11%. Comparing base (202a1d6) to head (4e49f8f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #822   +/-   ##
=======================================
  Coverage   86.11%   86.11%           
=======================================
  Files          71       71           
  Lines        3263     3263           
=======================================
  Hits         2810     2810           
  Misses        453      453           

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[FedericoNegri]

thanks