Reproducible build: failing to reproduce the build of the Rust SDK

Reproducible build seems to be broken because the Rust SDK build is not reproducible.

This has been reported by https://github.com/BarbossHack/reproducible/blob/master/history/ElementX-Android.md, see screenshot below:

According to @jmartinesp , it's probably because now we're stripping debug symbols to make the library way smaller and that is not done when building, but when publishing with an external script. This change has been introduce in Feb 6 by https://github.com/matrix-org/matrix-rust-components-kotlin/pull/91.

This does not impact the release of F-Droid, but, it should be good to make the build fully reproducible.