ci: run the merge checks on release branches, and fix the ptc-script-imports fixture (#7732)

* ci: run the merge checks on release branches too

All three `Policy` workflows filtered on `master`, so a pull request into `release/dsh-*`
got no `Master Change` and no `Pre-Merge Check`, and its review check only refreshed when
somebody submitted a review. The checks already take their base branch from the event, so
the filters now name the release branches as well.

* ci: limit the release branch filter to x.y.z

`release/dsh-*` also matched prerelease branches such as `release/dsh-0.1.2-alpha.4`;
the filter now spells the version digits, so only `release/dsh-x.y.z` counts.

* test(snapshot): carry the subagent identity section into the ptc-script-imports scenario

The runtime context gained a `subagent:identity` section and every session fixture but
this one was regenerated, so replay failed with a mismatch on the added section.

(cherry picked from commit c7a4119965cb26c69fd8fccbfd703c7d73351742)

---------

Co-authored-by: imccyu <[email protected]>

.github/workflows/pr-check-after-approve.yml

@@ -1,7 +1,7 @@
 name: Policy
 on:
   pull_request_target:
-    branches: [master]
+    branches: [master, 'release/dsh-[0-9]+.[0-9]+.[0-9]+']
     types: [opened, synchronize, reopened, ready_for_review]
   pull_request_review:
     types: [submitted, dismissed]

.github/workflows/pr-check-on-base-branch.yml

@@ -1,7 +1,7 @@
 name: Policy
 on:
   push:
-    branches: [master]
+    branches: [master, 'release/dsh-[0-9]+.[0-9]+.[0-9]+']
   workflow_dispatch:
 permissions: {}
 concurrency:

.github/workflows/pr-check-on-head-branch.yml

@@ -1,7 +1,7 @@
 name: Policy
 on:
   pull_request_target:
-    branches: [master]
+    branches: [master, 'release/dsh-[0-9]+.[0-9]+.[0-9]+']
     types: [opened, synchronize, reopened, ready_for_review, review_requested, auto_merge_enabled, labeled]
 permissions:
   contents: read