Valgrind failure with recent rustc

[molpopgen]

cargo +1.93.1 valgrind test is currently giving an error.

1.93.0 gives the same error

1.90.0, 1.91.0, and 1.92.0 give no such errors.

This is currently a road block to updating rust-toolchain.

[molpopgen]

It is possible that there is an issue only w/cargo-valgrind here. In the file where the leak is reported, commenting out each test one by one doesn't change the behavior until all are commented out.

[molpopgen]

I also see the same failure in demes-rs, which uses no FFI/malloc/etc.. This is definitely a false positive