Deny all default Clippy errors/warnings in github workflow

[kdarkhan]

When addressing this comment

You should at least trip the return which is not necessary here.

I noticed Clippy warnings such as warning: unneeded "return" statement and others like this do not produce non-zero status code which means the PR won't fail.

I am adding -D clippy::all in order to deny all default warnings to fail PRs.

Also adding a separate call to cargo clippy in directory i18n-helpers/fuzz because it is considered to be a separate workspace.

[mgeisler]

I've always been on the fence about Clippy — but I guess it's good to enable it for a shared project like this.

[kdarkhan]

I see, I haven't had much experience with Rust codebases. If this linter is over-restrictive I am ok with disabling the config as well.

[mgeisler]

I see, I haven't had much experience with Rust codebases. If this linter is over-restrictive I am ok with disabling the config as well.

Let's use this config for a while and see if it bothers us 😄