Update `protoc` version in build image

[ppodolsky]

Crate name

summa

Build failure link

https://docs.rs/crate/summa/0.7.1/builds/567648

Additional details

Hi guys!
I use prost-build to build proto files in build.rs and in its turn it uses system proto compiler. There are some fileds in my proto files that marked as optional. The optional has been added in proto 3.12 and stabilized in 3.15. So it seems that build machines/images contains outdated protoc

[syphar]

@ppodolsky the image being used is defined in https://github.com/rust-lang/crates-build-env , see also https://docs.rs/about/builds#missing-dependencies .

Any package in ubuntu focal can be added, so you can just create a PR to the repo.

( I'll review and deploy then)

[syphar]

( looking at https://github.com/rust-lang/crates-build-env/blob/master/linux/packages.txt it looks like we only have libprotoc17 in there currently)

[ppodolsky]

Yep, as usual I've found these pages immediately after had posted questions here :)

Looks like there is no an easy way because even 22.04 has too outdated protoc. The hackery way is to delete protoc binary before build and it will lead to building of vendored protoc in prost-build crate. But it is such a waste of resources and against the good sense.

[syphar]

until we have #315 your options are probably vendoring (as you stated), or conditional compilation if you don't need protoc for the docs.