test formerly broken serde_derive dependency

Author: RalfJung

test-cargo-miri/Cargo.lock

@@ -12,6 +12,7 @@ byteorder = "1.0"
 
 [dev-dependencies]
 rand = { version = "0.7", features = ["small_rng"] }
+serde_derive = "1.0" # not actually used, but exercises some unique code path (`--extern` .so file)
 
 [lib]
 test = false # test that this is respected (will show in the output)