Hi everyone, where is the best place to file an issue with the actual standard cell libraries (such as https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_sc_hd/), should I create a github issue in https://github.com/google/skywater-pdk and just link to the standard cell library?

I would think so. The googlesource things was really to workaround the github limits AFAIR.