Release on push to master instead of on closed PRs targeting it. (#9544)

This is safer than the prior approach, since it's safe by default: the
release workflows never get triggered for non-merged PRs, so there's no
possibility of a buggy conditional accidentally letting a workflow
proceed when it shouldn't have.

The only loss is that publishing no longer requires a `release` label on
the merged PR that bumps the version. We can add a separate CI step that
enforces that part as a condition for merging into `master`, if
desirable.

.github/workflows/_release.yml

@@ -13,9 +13,8 @@ env:
 
 jobs:
   if_release:
-    if: |
-        github.event.pull_request.merged == true
-        && contains(github.event.pull_request.labels.*.name, 'release')
+    # Disallow publishing from branches that aren't `master`.
+    if: github.ref == 'refs/heads/master'
     runs-on: ubuntu-latest
     defaults:
       run:

.github/workflows/langchain_experimental_release.yml

@@ -2,9 +2,7 @@
 name: libs/experimental Release
 
 on:
-  pull_request:
-    types:
-      - closed
+  push:
     branches:
       - master
     paths:
@@ -17,4 +15,4 @@ jobs:
       ./.github/workflows/_release.yml
     with:
       working-directory: libs/experimental
-    secrets: inherit
+    secrets: inherit

.github/workflows/langchain_release.yml

@@ -2,9 +2,7 @@
 name: libs/langchain Release
 
 on:
-  pull_request:
-    types:
-      - closed
+  push:
     branches:
       - master
     paths:
@@ -17,4 +15,4 @@ jobs:
       ./.github/workflows/_release.yml
     with:
       working-directory: libs/langchain
-    secrets: inherit
+    secrets: inherit