radicle: Add `tempfile` to dev-dependencies

In commit 2149770a4b the dependency
`tempfile` was made optional, and added to be enabled by the feature
flag `test`. However, the *tests of this crate itself* need the
dependency *unconditionally* as they want to create temporary
directories.

This was not noticed earlier, since the error does not surface when
the whole workspace is tested (`cargo test --workspace`), but only
when the crate itself is tested (`cargo test --package=radicle`),
because when testing the workspace, dependents of `radicle` will
enable the `test` feature flag.

crates/radicle/Cargo.toml

@@ -60,3 +60,4 @@ qcheck = { workspace = true }
 qcheck-macros = { workspace = true }
 radicle-cob = { workspace = true, features = ["stable-commit-ids"] }
 radicle-crypto = { workspace = true, features = ["test"] }
+tempfile = { workspace = true }