fix(third_party/crate2nix): run tests in debug mode

Behave like `cargo test` rather than `cargo test --release`.

Change-Id: Ie013d04ac68d7dec2a3b870fa9f0060a70a9635d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9621
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

tvix/Cargo.nix

@@ -10917,6 +10917,7 @@ rec {
               (
                 _: {
                   buildTests = true;
+                  release = false;
                 }
               );
             # If the user hasn't set any pre/post commands, we don't want to