c2rust: Use released version

[chrysn]

This reduces the dependency on a particular GitHub branch that I was already about to remove after immunant/c2rust#693 was done.

Still marked as a draft as it depends on immunant/c2rust#690 (but that has all its blockers gone already).

[kaspar030]

ACK.

[chrysn]

Reopening after accidentally having deleted the branch.

[chrysn]

Huh, saying that this is not where I'd have expected the error to show up would be putting it mildly -- I'm having a look at why this fails, but it may take a while.

[chrysn]

I have no clue what caused the build failure, and can not reproduce the issue locally (after building the container in podman and using BOARDS="arduino-uno esp32-wroom-32 hifive1b msb-430h native samr21-xpro" make -C examples/rust-gcoap BUILD_IN_DOCKER=1 DOCKER=podman DOCKER_IMAGE=localhost/riotbuild:latest buildtest to run the very test that CI should have run).

Let's see if it was a random glitch (like, file system error?), restarting the build test.

[chrysn]

Seems that builds break due to files left over from other runs. Switching to draft PR to prevent accidental merging just because a test happens to fix it.

[chrysn]

I suspect now that this is due to changes in some base image, and would break in master just as well.

I still can't make progress for lack of a way to reproduce it (works locally), so I'm triggering a master rebuild to cut down the space.