[DEVOPS-922] fix declaration of matplotlib dependency

it is an actual direct depedency, not only an override for conda

Author: sebhmg

pyproject.toml

@@ -62,6 +62,7 @@ version = "0.0.0.dev0"
 
 
 [tool.poetry.dependencies]
+matplotlib = "~3.8.4"  # also in simpeg
 numpy = "~1.26.0"
 pydantic = "^2.5.2"
 scipy = "~1.14.0"
@@ -98,7 +99,6 @@ channels = ['conda-forge']
 #---------------------------------------------------------------------------------
 Pillow = ">=10.3.0, <10.4.dev"  # from geoh5py
 h5py = ">=3.2.1, <4.0.dev"  # from geoh5py
-matplotlib = ">=3.8.4, <3.9.dev"  # from simpeg
 
 [tool.poetry.requires-plugins]
 poetry-dynamic-versioning = { version = ">=1.9.1,<2.0.0", extras = ["plugin"] }