Fix sdist to include rust build script (#13866)

* Fix sdist to include rust build script

Fixes #13851

* Newsfile

changelog.d/13866.bugfix

@@ -0,0 +1 @@
+Fix building from packaged sdist. Broke in v1.68.0rc1.

pyproject.toml

@@ -88,6 +88,7 @@ include = [
     { path = "Cargo.toml", format = "sdist" },
     { path = "rust/Cargo.toml", format = "sdist" },
     { path = "rust/Cargo.lock", format = "sdist" },
+    { path = "rust/build.rs", format = "sdist" },
     { path = "rust/src/**", format = "sdist" },
 ]
 exclude = [