Include .crates.toml in Rust example

Using the existing example, cargo install will error out after restoring a cache:
```
cargo install cargo-tarpaulin
    Updating crates.io index
error: binary `cargo-tarpaulin` already exists in destination
Add --force to overwrite
Error: Process completed with exit code 101.
```

`--force` is undesirable because it will recompile the binary.  Cargo is scared of the existing binary because it doesn't have enough information about it.  Including `~/.cargo/.crates.toml` coaxes it into being okay with the situation.

examples.md

@@ -591,6 +591,7 @@ whenever possible:
 - uses: actions/cache@v3
   with:
     path: |
+      ~/.cargo/.crates.toml
       ~/.cargo/bin/
       ~/.cargo/registry/index/
       ~/.cargo/registry/cache/