ci: in bot.yml, add checkout code and install go (#3224)

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pull request. -->

<details><summary>Contributors' checklist...</summary>

- [ ] Added new tests, or not needed, or not feasible
- [ ] Provided an example (e.g. screenshot) to aid review or the PR is
self-explanatory
- [ ] Updated the official documentation or not needed
- [ ] No breaking changes were made, or a `BREAKING CHANGE: xxx` message
was included in the description
- [ ] Added references to related issues and PRs
- [ ] Provided any useful hints for running manual tests
</details>

.github/workflows/bot.yml

@@ -42,6 +42,12 @@ jobs:
       pr-numbers: ${{ steps.pr-numbers.outputs.pr-numbers }}
 
     steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Install Go
+        uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
       - name: Generate matrix from event
         id: pr-numbers
         working-directory: contribs/github-bot