Add an empty ctest crate

A bit of a quirk of `release-plz` seems to be that it uses the latest
published stable Cargo.toml as the workspace root, which makes
publishing `ctest` a problem because it doesn't exist (and so isn't in
the workspace) with our published `libc`, instead only existing on
`main`.  Work around this by creating an empty crate named `ctest` so
the `libc-0.2` version of `Cargo.toml` lists it as a workspace member.

Link: release-plz/release-plz#2163

Author: tgross35

Cargo.toml

@@ -151,4 +151,7 @@ align = []
 use_std = ['std']
 
 [workspace]
-members = ["libc-test"]
+members = [
+    "ctest",
+    "libc-test",
+]

ctest/Cargo.toml

@@ -0,0 +1,10 @@
+# This is a dummy package so the published stable `libc` can have `ctest` in
+# the workspace, which works around <https://github.com/release-plz/release-plz/issues/2163>.
+
+[package]
+name = "ctest"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]

ctest/src/lib.rs

@@ -0,0 +1 @@
+