Prepare release of `3.2.0` (#637)

* Prepare release of `3.2.0`

* Add newline

* Do not change API outside of major version rev

* Change `main` to `master` in workflow

* yml -> yaml

.github/workflows/publish.yaml

@@ -0,0 +1,9 @@
+name: Publish
+on:
+  pull_request:
+    branches: [ master ]
+  push:
+    tags: [ '[0-9]+.[0-9]+.[0-9]+' ]
+jobs:
+  publish:
+    uses: dart-lang/ecosystem/.github/workflows/publish.yaml@main

CHANGELOG.md

@@ -1,4 +1,4 @@
-## 3.2.0-dev
+## 3.2.0
 
 * `ChannelOptions` now exposes `connectTimeout`, which is used on the 
   socket connect. This is used to specify the maximum allowed time to wait

pubspec.yaml

@@ -1,7 +1,7 @@
 name: grpc
 description: Dart implementation of gRPC, a high performance, open-source universal RPC framework.
 
-version: 3.2.0-dev
+version: 3.2.0
 
 repository: https://github.com/grpc/grpc-dart