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

Cargo.lock

@@ -2334,9 +2334,8 @@ dependencies = [
 
 [[package]]
 name = "ctor"
-version = "0.1.26"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6d2301688392eb071b0bf1a37be05c469d3cc4dbbd95df672fe28ab021e6a096"
+version = "0.1.20"
+source = "git+https://github.com/zed-industries/rust-ctor?rev=7f824cf6a7943885a649b579f33f9ac53f0d1db6#7f824cf6a7943885a649b579f33f9ac53f0d1db6"
 dependencies = [
  "quote",
  "syn 1.0.109",