open-source-silicon.dev

#57 Pins for some cells are missing `internal_power` group attribute in generated liberty files.
Issue opened by mithro
```
Warning: Line 170537, Cell 'sky130_fd_sc_hd__xor3_2', pin 'A', The pin 'A' does not have a internal_power group. (LBDB-607)
Warning: Line 170547, Cell 'sky130_fd_sc_hd__xor3_2', pin 'B', The pin 'B' does not have a internal_power group. (LBDB-607)
Warning: Line 170557, Cell 'sky130_fd_sc_hd__xor3_2', pin 'C', The pin 'C' does not have a internal_power group. (LBDB-607)

```
<https://github.com/google/skywater-pdk|google/skywater-pdk>