yosys: Use 4 digits in build string.
yosys: Use 4 digits in build string.

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