Address deprecated way of initializing AnnData in _scrublet.py

While running SnapAtac2 notebooks the following warning was
fairly frequently encountered when running `snap.pp.scrublet()`:

```
/usr/local/lib/python3.11/site-packages/anndata/_core/anndata.py:522: FutureWarning:

The dtype argument is deprecated and will be removed in late 2024.
```

It looks like the `anndata` project plans to deprecate and completely
remove the `dtype` argument to `AnnData` instantiation somewhat soon.
See: scverse/anndata@85162c7
See also: scverse/anndata#1126

This commit removes the `dtype` argument from `AnnData` instantiation
as it will be removed in future versions of `AnnData`.

snapatac2-python/python/snapatac2/preprocessing/_scrublet.py

@@ -255,7 +255,7 @@ def scrub_doublets_core(
     del count_matrix_sim
     gc.collect()
     _, evecs = spectral(
-        AnnData(X=merged_matrix, dtype=merged_matrix.dtype),
+        AnnData(X=merged_matrix),
         features=None,
         n_comps=n_comps,
         inplace=False,