Use newer Rust: nightly-2023-12-11. Apply "--locked" when installing sc-meta.

[andreibancioiu]

Unfortunately, it seems that upgrading Rust cannot be postponed too much.

https://github.com/multiversx/mx-sdk-rs/blob/master/.github/workflows/actions.yml#L18

Additionally, we should install sc-meta using --locked - to protect against eventual upcoming breaking changes (brought by direct or indirect dependencies of sc-meta):

cargo install multiversx-sc-meta --locked

As of 31st December of 2023, installation of sc-meta is broken due to a breaking change within the ahash library (dependency of hashbrown):

• https://t.me/MultiversXDevelopers/122082
• compile error: use of unstable library feature 'stdsimd' tkaitchuck/aHash#195