[PROPOSAL] Update Rust dependencies in Cargo.toml

[siliconwaffle]

So while trying to package ccextractor(master branch) for Fedora, I ran into a couple issues while trying to build with mock. Mainly bindgen-0.64.0 and iconv dependencies not being available in the Fedora repositories. Iconv is missing entirely, so I will have to submit that package to Fedora first before I can submit ccextractor. Anyways, bindgen is available but only specific versions, can this version be bumped up to 0.69.4 (0.68.0 is also acceptable as it is available in Fedora repos) without breaking anything? I don't know if updating the dependencies will break anything, but it will be practically impossible to package and submit to Fedora without this dependency issue being resolved first.