Libspa-sys rebuilds all the time

The libspa-sys crate is always rebuilt whenever cargo is invoked. Relevant cargo output:

Dirty libspa-sys v0.7.2 (https://gitlab.freedesktop.org/pipewire/pipewire-rs#26ed5ffd): the file `target/debug/build/libspa-sys-1a749fb816f6464a/out/static_fns.c` has changed (1698582990.772621875s, 2s after last build at 1698582988.230608054s)

The regression was introduced in commit 26ed5ffd, presumably because of requesting a rerun when the generated file changed. But I'm not sure if just dropping that breaks anything.