scripts: Allow conda build version to be forced.
scripts: Allow conda build version to be forced.

SymbiFlow/conda-packages,timvideos/conda-hdmi2usb-packages,SymbiFlow/conda-packages,litex-hub/litex-conda-eda,litex-hub/litex-conda-compilers,timvideos/conda-misoc-lm32,timvideos/conda-misoc-lm32,litex-hub/litex-conda-prog,timvideos/conda-hdmi2usb-packages