This version of go-cel expects to use golang/protobuf@v1.5, which 
implements the protobuf APIv1 but using the APIv2 implementation.
However, we can't use golang/protobuf@v1.3, because the code does
make use of the newer reflection API that is only present in APIv2.

In Debian, the genproto package was compiled using golang/protobuf@v1.3,
which lacks support for the reflection API. Therefore, this package ships
a minimized vendored copy of the google/genproto sources that has been
compiled with golang/protobuf@v1.5.

Specifically, sources were copied from
https://github.com/googleapis/go-genproto/tree/715cce707fb0474ad6718c6a213fc78dc168aff9

This vendored copy should be removed when we update the package
golang-google-genproto-dev to a version that has been compiled with
golang/protobuf@v1.5.

See this thread for the reasoning:
https://lists.debian.org/debian-go/2022/11/msg00068.html
