pin setuptools below 69.3 and prepare for "build" for releases

Change-Id: Ib70446cc3c7d7d8acb264ffa2237a0c7aac5a0f5

Author: zzzeek

pyproject.toml

@@ -1,6 +1,10 @@
 [build-system]
-requires = ["setuptools>=61.0"]
 build-backend = "setuptools.build_meta"
+requires = [
+    # avoid moving to https://github.com/pypa/setuptools/issues/3593
+    # until we're ready
+    "setuptools>=61.0,<69.3",
+]
 
 [project]
 name = "awaitlet"