ci(restore-node): corepack enable to accommodate Endo (#9306)

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## Description

Although nightly Endo integration tests have not yet been fully vetted,
this PR does at least prevent [the following
error](https://github.com/Agoric/agoric-sdk/actions/runs/8874236604/job/24361339426#step:6:27):
```
/home/runner/endo /home/runner/work/agoric-sdk/agoric-sdk
Switched to a new branch 'lerna-publish'
error This project's package.json defines "packageManager": "[email protected]". However the current global version of Yarn is 1.22.22.

Presence of the "packageManager" field indicates that the project is meant to be used with Corepack, a tool included by default with all official Node.js distributions starting from 16.9 and 14.19.
```

### Security Considerations

CI only.

### Scaling Considerations

No impact.

### Documentation Considerations

n/a, internal CI configuration.

### Testing Considerations

Tested nightly against latest Endo repository.

### Upgrade Considerations

n/a

.github/actions/restore-node/action.yml

@@ -114,6 +114,8 @@ runs:
           ${{ inputs.path }}/endo-sha.txt
     - uses: kenchan0130/actions-system-info@master
       id: system-info
+    - run: corepack enable
+      shell: bash
     - name: restore built files
       id: built
       uses: actions/cache@v4

.github/workflows/integration.yml

@@ -243,9 +243,7 @@ jobs:
           ignore-endo-branch: 'true'
         id: restore-node
       - name: setup a3p-integration
-        run: |
-          corepack enable
-          yarn install
+        run: yarn install
         working-directory: a3p-integration
       - name: verify SDK image didn't change
         # In the future when we can rebuild the SDK image with resolved endo packages, it would