chore: add boltons to pixi/conda envs (#2242)

After modflowpy/flopy@c5b5a41 flopy needs boltons for code generation. Would ideally install transitively thru the optional dependency group but currently flopy is installed from github. And boltons is useful enough to warrant addition IMO

Author: wpbonelli

environment.yml

@@ -6,6 +6,7 @@ channels:
 
 dependencies:
   - python>=3.10
+  - boltons
   - appdirs
   - cffconvert
   - codespell