Update actions/checkout action to v5 (#535)

> [!NOTE]
> Mend has cancelled [the proposed
renaming](https://redirect.github.com/renovatebot/renovate/discussions/37842)
of the Renovate GitHub app being renamed to `mend[bot]`.
> 
> This notice will be removed on 2025-10-07.

<hr>

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://redirect.github.com/actions/checkout) |
action | major | `v4` -> `v5` |

---

### Release Notes

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

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

[Compare
Source](https://redirect.github.com/actions/checkout/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 is behind base branch, 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/bazel-contrib/toolchains_llvm).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0MS42Ni4yIiwidXBkYXRlZEluVmVyIjoiNDEuMTMxLjkiLCJ0YXJnZXRCcmFuY2giOiJtYXN0ZXIiLCJsYWJlbHMiOltdfQ==-->

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/release.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
       - name: Prepare release
         run: .github/workflows/release_prep.sh > release_notes.txt
       - name: Release

.github/workflows/tests.yml

@@ -20,7 +20,7 @@ jobs:
       contents: read # For repo checkout
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
       - name: Trunk Check
         uses: trunk-io/trunk-action@v1
   test:
@@ -33,7 +33,7 @@ jobs:
         bzlmod: [true, false]
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - if: startsWith(matrix.os, 'ubuntu')
         run: tests/scripts/ubuntu_install_libtinfo.sh
       - run: sudo rm -rf /usr/share/dotnet /usr/local/lib/android
@@ -45,7 +45,7 @@ jobs:
   toolchain_test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - name: Test
         env:
           USE_BAZEL_VERSION: latest
@@ -61,7 +61,7 @@ jobs:
         bzlmod: [true, false]
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - if: startsWith(matrix.os, 'ubuntu')
         run: tests/scripts/ubuntu_install_libtinfo.sh
       - name: Test
@@ -87,7 +87,7 @@ jobs:
         bzlmod: [true, false]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - run: sudo rm -rf /usr/share/dotnet /usr/local/lib/android
       - name: Test
         env:
@@ -100,7 +100,7 @@ jobs:
         bzlmod: [true, false]
     runs-on: macos-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - name: Test
         env:
           USE_BZLMOD: ${{ matrix.bzlmod }}
@@ -112,7 +112,7 @@ jobs:
         bzlmod: [true, false]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - run: tests/scripts/ubuntu_install_libtinfo.sh
       - name: Test
         env:
@@ -125,7 +125,7 @@ jobs:
         bzlmod: [true, false]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - run: tests/scripts/ubuntu_install_libtinfo.sh
       - name: Download and Extract LLVM distribution
         env: