ci: run AWS fork workflows on cortex-main instead of main

.github/workflows/aws-changes.yml

@@ -1,7 +1,7 @@
 name: aws-changes
 on:
   push:
-    branches: [main]
+    branches: [cortex-main]
   schedule:
     - cron: "0 8 * * MON"     # catches upstream-absorbed changes retiring without a merge
   workflow_dispatch: {}
@@ -33,16 +33,16 @@ jobs:
             --upstream-ref "upstream/$UPSTREAM_BRANCH" \
             --repo-url "https://github.com/$REPO" \
             --source-sha "$SOURCE_SHA" \
-            --source-ref "refs/heads/main" > /tmp/publish/AWS-CHANGES.md
+            --source-ref "refs/heads/cortex-main" > /tmp/publish/AWS-CHANGES.md
           cat > /tmp/publish/README.md <<'EOF'
           # AWS-CHANGES publish branch
 
           This orphan branch carries only the auto-generated manifest of AWS changes
           this fork holds on top of upstream Alertmanager: **[AWS-CHANGES.md](AWS-CHANGES.md)**.
 
-          It is regenerated by the `aws-changes` workflow on every push to `main`
+          It is regenerated by the `aws-changes` workflow on every push to `cortex-main`
           (plus weekly, to retire changes upstream has absorbed). Nothing here is
-          edited by hand, and no pull request is involved. Code lives on `main`.
+          edited by hand, and no pull request is involved. Code lives on `cortex-main`.
           EOF
       - name: Publish to the manifest branch
         env:

.github/workflows/aws-fork-ci.yml

@@ -1,9 +1,9 @@
 name: aws-fork-ci
 on:
   pull_request:
-    branches: [main, "release-*"]
+    branches: [cortex-main, "release-*"]
   push:
-    branches: [main]
+    branches: [cortex-main]
 jobs:
   build-and-test:
     runs-on: ubuntu-latest

.github/workflows/trailer-lint.yml

@@ -1,7 +1,7 @@
 name: trailer-lint
 on:
   pull_request:
-    branches: [main]
+    branches: [cortex-main]
 jobs:
   trailer-lint:
     if: ${{ !startsWith(github.head_ref, 'sync/upstream-') }}