_cargo/config: enable sparse-registry

[ERROR rust_analyzer::lsp_utils] rust-analyzer failed to load workspace: Failed to read Cargo metadata from Cargo.toml file /home/yous.zhouys/git-repo/.../Cargo.toml, Some(Version { major: 1, minor: 65, patch: 0, pre: Prerelease("nightly") }): Failed to run `"cargo" "metadata" "--format-version" "1" "--manifest-path" "/home/yous.zhouys/git-repo/.../Cargo.toml" "--filter-platform" "x86_64-unknown-linux-gnu"`: `cargo metadata` exited with an error: error: failed to get `anyhow` as a dependency of package `... v0.1.0 (/home/yous.zhouys/git-repo/...../.../...)`

Caused by:
  failed to load source for dependency `anyhow`

Caused by:
  Unable to update registry `crates-io`

Caused by:
  usage of sparse registries requires `-Z sparse-registry`

data/_cargo/config

@@ -12,3 +12,7 @@ registry = "https://mirrors.sjtug.sjtu.edu.cn/git/crates.io-index"
 
 [source.rustcc]
 registry = "git://crates.rustcc.cn/crates.io-index"
+
+# https://doc.rust-lang.org/cargo/reference/unstable.html
+[unstable]
+sparse-registry = true