Use a fork of ctor to silence warnings generated by macro (#3275)

This PR switches us over to a fork of `ctor` that contains the fixes
from https://github.com/mmastrac/rust-ctor/pull/295, backported to our
current version of `ctor` (v0.1.20).

Once 1) the `ctor` maintainer publishes a new version with that change
and 2) we're ready to upgrade to the latest version of `ctor` we can
switch back to the mainline version.

Release Notes:

- N/A

crates/zed/Cargo.toml

@@ -84,7 +84,7 @@ async-recursion = "0.3"
 async-trait.workspace = true
 backtrace = "0.3"
 chrono = "0.4"
-ctor = "0.1.20"
+ctor.workspace = true
 env_logger.workspace = true
 futures.workspace = true
 ignore = "0.4"