Fix the use of removed numpy types

[bwroblew]

Both np.bool and np.unicode were deprecated in numpy 1.20.0 and removed in numpy 1.24.0.
Since release notes of 1.20.0 say that np.bool is identical to bool and np.unicode is identical to str, I changed them that way.

Confirmed using numpy 1.23.5:

>>> np.__version__
'1.23.5'
>>> np.unicode is str
<stdin>:1: DeprecationWarning: `np.unicode` is a deprecated alias for `np.compat.unicode`. To silence this warning, use `np.compat.unicode` by itself. In the likely event your code does not need to work on Python 2 you can use the builtin `str` for which `np.compat.unicode` is itself an alias. Doing this will not modify any behaviour and is safe. If you specifically wanted the numpy scalar type, use `np.str_` here.
Deprecated in NumPy 1.20; for more details and guidance: https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations
True
>>> np.bool is bool
<stdin>:1: DeprecationWarning: `np.bool` is a deprecated alias for the builtin `bool`. To silence this warning, use `bool` by itself. Doing this will not modify any behavior and is safe. If you specifically wanted the numpy scalar type, use `np.bool_` here.
Deprecated in NumPy 1.20; for more details and guidance: https://numpy.org/devdocs/release/1.20.0-notes.html#deprecations
True

In numpy 1.24.0 both types don't exist anymore:

>>> np.__version__
'1.24.0'
>>> np.unicode       
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "[...]/python3.8/site-packages/numpy/__init__.py", line 284, in __getattr__
    raise AttributeError("module {!r} has no attribute "
AttributeError: module 'numpy' has no attribute 'unicode'
>>> np.bool
<stdin>:1: FutureWarning: In the future `np.bool` will be defined as the corresponding NumPy scalar.  (This may have returned Python scalars in past versions.
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "[...]/python3.8/site-packages/numpy/__init__.py", line 284, in __getattr__
    raise AttributeError("module {!r} has no attribute "
AttributeError: module 'numpy' has no attribute 'bool'

[codecov]

Codecov Report

Merging #6495 (15d4c2f) into master (cc596b8) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #6495   +/-   ##
=======================================
  Coverage   85.64%   85.64%           
=======================================
  Files         405      405           
  Lines       22450    22450           
=======================================
  Hits        19227    19227           
  Misses       3223     3223           

Impacted Files	Coverage Δ
torch_geometric/data/dataset.py	91.77% <100.00%> (ø)

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[rusty1s]

Amazing, thank you!