fix windows build

8 jobs for win in 7 minutes and 21 seconds (queued for 3 seconds)
Name Stage Failure
failed
minimal-windows Test
base                     C:\Users\build\Miniconda3
pystencils_dev C:\Users\build\Miniconda3\envs\pystencils_dev

$ conda install `grep -Eo 'sympy[>=]+[0-9\.]+' setup.py | sed 's/>/=/g'`

EnvironmentLocationNotFound: Not a conda environment: C:\Users\build\Miniconda3\envs\pystencils_dev

Cleaning up file based variables
ERROR: Job failed: Process exited with status 1