fix(ci): Fix cross-compilation (#11687)

In https://github.com/vectordotdev/vector/pull/11674 I moved
cargo/config to cargo/config.toml but neglected CI was modifying this
file which caused it to write a new cargo/config and ignore the
cargo/config.toml. I just removed that modification of cargo/config and
replaced it by using the environment variable controlling incremental
compilation.

Signed-off-by: Jesse Szwedko <jesse@szwedko.me>