Issue with aggregate_duplicate_var: np.max throws TypeError: 'coo_matrix' object is not subscriptable

[ryan2han]

Description of the bug

I encountered an issue when using aggregate_duplicate_var on an AnnData object where the aggregation function (aggr_fun) is set to np.max.
While using np.mean works as expected, setting aggr_fun=np.max results in the following error:

TypeError: 'coo_matrix' object is not subscriptable

adata = sc.read_10x_h5(files[0])
UserWarning: Variable names are not unique. To make them unique, call `.var_names_make_unique`.
  utils.warn_names_duplicates("var")

adata.X
<9132x33670 sparse matrix of type '<class 'numpy.int64'>'
  	with 9701929 stored elements in Compressed Sparse Row format>

def aggregate_duplicate_var(adata, aggr_fun=np.mean):
    retain_var = ~adata.var_names.duplicated(keep="first")
    duplicated_var = adata.var_names[adata.var_names.duplicated()].unique()
    if len(duplicated_var):
        for var in duplicated_var:
            mask = adata.var_names == var
            var_aggr = aggr_fun(adata.X[:, mask], axis=1)[:, np.newaxis]
            adata.X[:, mask] = np.repeat(var_aggr, np.sum(mask), axis=1)

        adata_dedup = adata[:, retain_var].copy()
        return adata_dedup
    else:
        return adata

adata = aggregate_duplicate_var(adata,aggr_fun=np.max)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[24], [line 1](vscode-notebook-cell:?execution_count=24&line=1)
----> [1](vscode-notebook-cell:?execution_count=24&line=1) adata = aggregate_duplicate_var(adata,aggr_fun=np.max)

Cell In[23], [line 7](vscode-notebook-cell:?execution_count=23&line=7)
      [5](vscode-notebook-cell:?execution_count=23&line=5) for var in duplicated_var:
      [6](vscode-notebook-cell:?execution_count=23&line=6)     mask = adata.var_names == var
----> [7](vscode-notebook-cell:?execution_count=23&line=7)     var_aggr = aggr_fun(adata.X[:, mask], axis=1)[:, np.newaxis]
      [8](vscode-notebook-cell:?execution_count=23&line=8)     adata.X[:, mask] = np.repeat(var_aggr, np.sum(mask), axis=1)
     [10](vscode-notebook-cell:?execution_count=23&line=10) adata_dedup = adata[:, retain_var].copy()

TypeError: 'coo_matrix' object is not subscriptable
···


### Command used and terminal output

```console

Relevant files

No response

System information

OS: ubuntu20.04
numpy: 1.23.5
scipy: 1.11.4
scanpy: 1.9.6