Fix overly relaxed version requirement on NumPy (#1472)

Since commit 489b1fd, this package has been using
`numpy.typing.DTypeLike`, which was only added in [NumPy 1.20][1].

[1]: https://numpy.org/doc/stable/release/1.20.0-notes.html#numpy-is-now-typed

Co-authored-by: troiganto <troiganto@proton.me>
Co-authored-by: Antonin RAFFIN <antonin.raffin@ensta.org>

docs/misc/changelog.rst

@@ -35,6 +35,7 @@ New Features:
 Bug Fixes:
 ^^^^^^^^^^
 - Fixed ``VecExtractDictObs`` does not handle terminal observation (@WeberSamuel)
+- Set NumPy version to ``>=1.20`` due to use of ``numpy.typing`` (@troiganto)
 - Fixed loading DQN changes ``target_update_interval`` (@tobirohrer)
 
 Deprecations:
@@ -1331,4 +1332,4 @@ And all the contributors:
 @carlosluis @arjun-kg @tlpss
 @Melanol @qgallouedec @francescoluciano @jlp-ue @burakdmb @timothe-chaumont @honglu2875
 @anand-bala @hughperkins @sidney-tio @AlexPasqua @dominicgkerr @Akhilez @Rocamonde @tobirohrer @ZikangXiong
-@DavyMorgan @luizapozzobon @Bonifatius94 @theSquaredError @harveybellini @DavyMorgan @FieteO @jonasreiher @npit @WeberSamuel
+@DavyMorgan @luizapozzobon @Bonifatius94 @theSquaredError @harveybellini @DavyMorgan @FieteO @jonasreiher @npit @WeberSamuel @troiganto

setup.py

@@ -103,7 +103,7 @@
     package_data={"stable_baselines3": ["py.typed", "version.txt"]},
     install_requires=[
         "gymnasium==0.28.1",
-        "numpy",
+        "numpy>=1.20",
         "torch>=1.11",
         'typing_extensions>=4.0,<5; python_version < "3.8.0"',
         # For saving models