chore(deps): update actions/checkout action to v6.1.0 (#14101)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://redirect.github.com/actions/checkout) |
action | minor | `v6.0.3` → `v6.1.0` |

---

> [!WARNING]
> Some dependencies could not be looked up. Check the [Dependency
Dashboard](../issues/7649) for more information.

---

### Release Notes

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

###
[`v6.1.0`](https://redirect.github.com/actions/checkout/compare/v6.0.3...v6.1.0)

[Compare
Source](https://redirect.github.com/actions/checkout/compare/v6.0.3...v6.1.0)

</details>

---

### Configuration

📅 **Schedule**: (UTC)

- 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.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- 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/google-cloud-java).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0NC4zMi42IiwidXBkYXRlZEluVmVyIjoiNDQuMzIuNiIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOltdfQ==-->

Author: renovate-bot

.github/workflows/ci.yaml

@@ -35,7 +35,7 @@ jobs:
       # runnable is true if there are changes outside the .github/workflows directory OR if ci.yaml itself (or kokoro scripts) is modified.
       runnable: ${{ fromJSON(steps.filter.outputs.all_count) > fromJSON(steps.filter.outputs.workflows_count) || fromJSON(steps.filter.outputs.ci_count) > 0 }}
     steps:
-    - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+    - uses: actions/checkout@d23441a48e516b6c34aea4fa41551a30e30af803 # v6.1.0
       with:
         persist-credentials: false
       # Use this action, rather than a file filter so that we can make this
@@ -125,7 +125,7 @@ jobs:
     outputs:
       packages: ${{ steps.filter.outputs.changes }}
     steps:
-    - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+    - uses: actions/checkout@d23441a48e516b6c34aea4fa41551a30e30af803 # v6.1.0
       with:
         persist-credentials: false
     - uses: dorny/paths-filter@fbd0ab8f3e69293af611ebaee6363fc25e6d187d # v4.0.1