Prepare releaes 4.12.0a1 (#398)

Author: JelleZijlstra

CHANGELOG.md

@@ -1,4 +1,7 @@
-# Unreleased
+# Release 4.12.0a1
+
+This release primarily tests a revised release workflow. If all goes
+well, release 4.12.0rc1 will follow soon.
 
 - Backport the `typing.NoDefault` sentinel object from Python 3.13.
   TypeVars, ParamSpecs and TypeVarTuples without default values now have

pyproject.toml

@@ -6,7 +6,7 @@ build-backend = "flit_core.buildapi"
 # Project metadata
 [project]
 name = "typing_extensions"
-version = "4.11.0"
+version = "4.12.0a1"
 description = "Backported and Experimental Type Hints for Python 3.8+"
 readme = "README.md"
 requires-python = ">=3.8"