Requests_cache not included in install

[willu47]

$ research_index
/home/pi/repositories/research_index_backend/src/research_index_backend/create_graph_from_doi.py:45: SyntaxWarning: invalid escape sequence '\d'
  PATTERN = compile("10.\d{4,9}\/[-._;()\/:A-Z0-9]+", IGNORECASE)
Traceback (most recent call last):
  File "/home/pi/mambaforge/envs/research_index/bin/research_index", line 5, in <module>
    from research_index_backend import entry_point
  File "/home/pi/repositories/research_index_backend/src/research_index_backend/__init__.py", line 1, in <module>
    from .create_graph_from_doi import entry_point
  File "/home/pi/repositories/research_index_backend/src/research_index_backend/create_graph_from_doi.py", line 27, in <module>
    import requests_cache
ModuleNotFoundError: No module named 'requests_cache'