ci: pin actions/github-script to immutable SHA and upgrade to v9.0.0 (#6016)

This updates `ci.yml` to remove mutable `actions/github-script@v7`
references and align them with the repository’s SHA-pinned Actions
policy. All four usages are now pinned to the v9.0.0 commit SHA.

- **What changed**
- Replaced 4 instances of `actions/github-script@v7` in
`.github/workflows/ci.yml`
- Pinned each to
`actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 #
v9.0.0`

- **Scope**
  - Only workflow definition changes in `.github/workflows/ci.yml`
  - No runtime application logic or test code changes

```yaml
# before
uses: actions/github-script@v7

# after
uses: actions/github-script@3a2844b # v9.0.0
```

Author: lpcox

.github/workflows/ci.yml

@@ -165,7 +165,7 @@ jobs:
       contents: read
     steps:
       - name: Trigger smoke-copilot workflow for PR
-        uses: actions/github-script@v7
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
         with:
           script: |
             await github.rest.actions.createWorkflowDispatch({
@@ -184,7 +184,7 @@ jobs:
       actions: write
     steps:
       - name: Trigger smoke-copilot workflow
-        uses: actions/github-script@v7
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
         with:
           script: |
             await github.rest.actions.createWorkflowDispatch({
@@ -203,7 +203,7 @@ jobs:
       actions: write
     steps:
       - name: Trigger large-payload-tester workflow
-        uses: actions/github-script@v7
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
         with:
           script: |
             await github.rest.actions.createWorkflowDispatch({
@@ -222,7 +222,7 @@ jobs:
       actions: write
     steps:
       - name: Trigger language-support-tester workflow
-        uses: actions/github-script@v7
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
         with:
           script: |
             await github.rest.actions.createWorkflowDispatch({