Add an underscore after a link, as suggested by https://github.com/UPPMAX/HPC-python/actions/runs/23788615334/job/69318020341#step:10:12

Author: richelbilderbeek

docs/day3/big_data.rst

@@ -570,7 +570,7 @@ An overview of common data formats
      - ❌
      - 🟨
 
-   * - :ref:`Graph formats <https://gephi.org/users/supported-graph-formats/>`
+   * - :ref:`Graph formats <https://gephi.org/users/supported-graph-formats/>`_
      - 🟨
      - 🟨
      - ❌