fix visium_hd reader

[Mira-Kreuzer]

turns gex_only=False

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.65%. Comparing base (433014e) to head (ef5afeb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #389   +/-   ##
=======================================
  Coverage   61.65%   61.65%           
=======================================
  Files          27       27           
  Lines        3161     3161           
=======================================
  Hits         1949     1949           
  Misses       1212     1212           

Files with missing lines	Coverage Δ
src/spatialdata_io/readers/visium_hd.py	75.16% <100.00%> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.