fix: Add pip as explicit dep in environment.yml to prevent warning (#2574)

Removes this warning:

> Warning: you have pip-installed dependencies in your environment file,
but you do not list pip itself as one of your conda dependencies. Conda
may not use the correct pip to install your packages, and they may end
up in the wrong place. Please add an explicit pip dependency. I'm adding
one for you, but still nagging you.

Co-authored-by: Matt Robinson <mrobinson@unstructured.io>

environment.yml

@@ -12,6 +12,7 @@ dependencies:
   - pywin32
   - poppler
   - torchvision
+  - pip
   - pip:
     - huggingface-hub
     - layoutparser