RocksDB is recompiled despite caching

[tillrohrmann]

Currently, our CI is recompiling RocksDB despite being cached via Swatinem/rust-cache. The problem is caused by Swatinem/rust-cache not caching the .cargo/registry/src/librocksdb-sys-*/rocksdb

See:

rust-rocksdb/rust-rocksdb#574
Swatinem/rust-cache#100

Currently, people fork the Swatinem/rust-cache action to also include caching the registry/src/librocksdb-sys-* directory:

https://github.com/bmwill/rust-cache
https://github.com/radixdlt/rust-cache/commits/allow_registry_src_caching