ollijh has requested that we bump the default Gradle version to 9 as part of this PR, but to me this seems premature. I would think that the individual package maintainers should update individually and perhaps follow what the upstream packages are doing. And projects that use non-built-in plugins often need to wait for plugins to be updated.

I tried bumping three packages selected arbitrarily and none of them worked. See https://github.com/NixOS/nixpkgs/pull/421047#issuecomment-3189716199