Update pyiron_base to 0.6.15

[jan-janssen]

No description provided.

[jan-janssen]

          from mp_api.client import MPRester
        File "/usr/share/miniconda3/envs/my-env/lib/python3.11/site-packages/mp_api/client/__init__.py", line 7, in <module>
          from .core import MPRestError
        File "/usr/share/miniconda3/envs/my-env/lib/python3.11/site-packages/mp_api/client/core/__init__.py", line 3, in <module>
          from .client import BaseRester, MPRestError
        File "/usr/share/miniconda3/envs/my-env/lib/python3.11/site-packages/mp_api/client/core/client.py", line 24, in <module>
          from emmet.core.utils import jsanitize
        File "/usr/share/miniconda3/envs/my-env/lib/python3.11/site-packages/emmet/core/utils.py", line 11, in <module>
          from pydantic import BaseModel
        File "/usr/share/miniconda3/envs/my-env/lib/python3.11/site-packages/pydantic/__init__.py", line 372, in __getattr__
          module = import_module(module_name, package=package)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/usr/share/miniconda3/envs/my-env/lib/python3.11/importlib/__init__.py", line 126, in import_module
          return _bootstrap._gcd_import(name[level:], package, level)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        File "/usr/share/miniconda3/envs/my-env/lib/python3.11/site-packages/pydantic/main.py", line 13, in <module>
          from pydantic_core import PydanticUndefined
      ImportError: cannot import name 'PydanticUndefined' from 'pydantic_core' (unknown location)
      [end of output]

[jan-janssen]

The issue was already reported in conda-forge/pydantic-core-feedstock#79 and seems to be fixed now.