Add entry for google.golang.org/protobuf

[MikaelUrankar]

Seen with sysutils/gotop (https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=247049)

# Mirrors for the following packages are not currently known, please look them up and handle these tuples manually:
#       ::v1.21.0:group_name/vendor/google.golang.org/protobuf
protocolbuffers:protobuf-go:v1.21.0:protocolbuffers_protobuf_go/vendor/google.golang.org/protobuf

According to https://pkg.go.dev/mod/google.golang.org/protobuf@v1.24.0 the repo is here: Repository: https://github.com/protocolbuffers/protobuf-go

[dmgk]

Merged, thanks!