ci: bump to cbindgen v0.29.3

[cyphar]

This version added support for C23 fixed-type enum syntax, which caused
our CI to break as the output of cbindgen changed. To avoid this
happening in the future, lock the cbindgen version in CI.

Signed-off-by: Aleksa Sarai aleksa@amutable.com

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[cyphar]

I opened this issue to help show the issue with mozilla/cbindgen#1156. For now, we will need to pin an older version.

[martinpitt]

#408 is vaguely related to this. However, this PR is blocked on the Python bindings. However, the Go failure would not have shown up here, as CI runs on Ubuntu latest (i.e. 24.04 LTS) whose gcc still defaults to gcc17. But that this only true as long as emilio's suggestion in mozilla/cbindgen#1156 of "defaulting to true with the ifdefs removed altogether" does not land. If/once it actually does, generated headers use the enum spelling unconditionally, so so type ProcBase C.pathrs_proc_base_t breaks on every compiler and -std=gnu17 stops being a workaround for anyone, and it will also start failing on our ubuntu-latest CI runs. Then #408 becomes much more urgent.