core: use "data-types" instead of "data types"

From the reference[^0]:

> Note: crates.io allows a maximum of 5 keywords. Each keyword must be
> ASCII text, have at most 20 characters, start with an alphanumeric
> character, and only contain letters, numbers, _, - or +.

[0]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-keywords-field

crates/radicle-core/Cargo.toml

@@ -6,7 +6,7 @@ repository.workspace = true
 version = "0.1.0"
 edition.workspace = true
 license.workspace = true
-keywords = ["radicle", "git", "data types"]
+keywords = ["radicle", "git", "data-types"]
 rust-version.workspace = true
 
 # For documentation of features refer to the module documentation in `./lib.rs`