fix index cannot be reshaped with inner join

[melonora]

closes #829

There was a problem when a mutable copy was created when performing an inner join. This was due to slicing using an Index which did not have the method .reshape. This is fixed in this PR by converting it to a list.

Tested on the squidpy notebook.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.72%. Comparing base (4630fa1) to head (00caed6).
Report is 35 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #832   +/-   ##
=======================================
  Coverage   91.72%   91.72%           
=======================================
  Files          46       46           
  Lines        7166     7166           
=======================================
  Hits         6573     6573           
  Misses        593      593           

Files with missing lines	Coverage Δ
src/spatialdata/_core/query/relational_query.py	90.78% <100.00%> (ø)

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