DOC: trivial rst fix to whats_new.rst (scikit-learn#7511)

Fix for proper rendering

Author: GaelVaroquaux

doc/whats_new.rst

@@ -296,7 +296,7 @@ Enhancements
      :func:`utils.sparse_func.incr_mean_variance_axis` by supporting cython
      fused types. By `YenChen Lin`_.
 
-   - The :func: `ignore_warnings` now accept a category argument to ignore only
+   - The :func:`ignore_warnings` now accept a category argument to ignore only
      the warnings of a specified type. By `Thierry Guillemot`_.
 
    - The new ``cv_results_`` attribute of :class:`model_selection.GridSearchCV`