REL: Declare numpy<1.24 requirement

In numpy 1.24, dtype=object has to be specified when creating
a ragged array. In fissa, we were reliant on that being automatically
detected.

requirements.txt

@@ -1,6 +1,6 @@
 future>=0.16.0
 joblib>=0.14.1
-numpy>=1.13.0,<2.0
+numpy>=1.13.0,<1.24
 Pillow>=4.3.0
 read-roi>=1.5.0; python_version>='3.0'
 scikit-image>=0.13.0