chore(deps): update github actions (major) (googleapis#2700)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://redirect.github.com/actions/checkout) |
action | major | `v4` → `v6` |
|
[actions/download-artifact](https://redirect.github.com/actions/download-artifact)
| action | major | `v4` → `v8` |
|
[actions/upload-artifact](https://redirect.github.com/actions/upload-artifact)
| action | major | `v4` → `v7` |

---

### Release Notes

<details>
<summary>actions/checkout (actions/checkout)</summary>

### [`v6`](https://redirect.github.com/actions/checkout/compare/v5...v6)

[Compare
Source](https://redirect.github.com/actions/checkout/compare/v5...v6)

### [`v5`](https://redirect.github.com/actions/checkout/compare/v4...v5)

[Compare
Source](https://redirect.github.com/actions/checkout/compare/v4...v5)

</details>

<details>
<summary>actions/download-artifact (actions/download-artifact)</summary>

###
[`v8`](https://redirect.github.com/actions/download-artifact/compare/v7...v8)

[Compare
Source](https://redirect.github.com/actions/download-artifact/compare/v7...v8)

###
[`v7`](https://redirect.github.com/actions/download-artifact/compare/v6...v7)

[Compare
Source](https://redirect.github.com/actions/download-artifact/compare/v6...v7)

###
[`v6`](https://redirect.github.com/actions/download-artifact/compare/v5...v6)

[Compare
Source](https://redirect.github.com/actions/download-artifact/compare/v5...v6)

###
[`v5`](https://redirect.github.com/actions/download-artifact/compare/v4...v5)

[Compare
Source](https://redirect.github.com/actions/download-artifact/compare/v4...v5)

</details>

<details>
<summary>actions/upload-artifact (actions/upload-artifact)</summary>

###
[`v7`](https://redirect.github.com/actions/upload-artifact/compare/v6...v7)

[Compare
Source](https://redirect.github.com/actions/upload-artifact/compare/v6...v7)

###
[`v6`](https://redirect.github.com/actions/upload-artifact/compare/v5...v6)

[Compare
Source](https://redirect.github.com/actions/upload-artifact/compare/v5...v6)

###
[`v5`](https://redirect.github.com/actions/upload-artifact/compare/v4...v5)

[Compare
Source](https://redirect.github.com/actions/upload-artifact/compare/v4...v5)

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined),
Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you
are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the
rebase/retry checkbox.

👻 **Immortal**: This PR will be recreated if closed unmerged. Get
[config
help](https://redirect.github.com/renovatebot/renovate/discussions) if
that's undesired.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

This PR was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/googleapis/genai-toolbox).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0My41OS4wIiwidXBkYXRlZEluVmVyIjoiNDMuNTkuMCIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOltdfQ==-->

Author: renovate-bot

.github/workflows/docs_preview_build.yaml

@@ -77,7 +77,7 @@ jobs:
           echo $PR_NUMBER > ../artifact-payload/pr_number.txt
 
       - name: Upload Artifact
-        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
+        uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7
         with:
           name: docs-preview-data
           path: artifact-payload/

.github/workflows/docs_preview_deploy.yaml

@@ -45,10 +45,10 @@ jobs:
       cancel-in-progress: true
     steps:
       - name: Checkout base repository
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4 
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6 
 
       - name: Download Artifact
-        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8
         with:
           name: docs-preview-data
           github-token: ${{ secrets.GITHUB_TOKEN }}