Bump actions/checkout from 4 to 5

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 5.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v5)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/merge-to-main.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     # checkout to the commit that has been pushed
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v5
 
     - name: Setup Hugo
       uses: peaceiris/actions-hugo@v3.0.0

.github/workflows/pull-request.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     # checkout to the commit that has been pushed
-    - uses: actions/checkout@v4.1.1
+    - uses: actions/checkout@v5
 
     - name: Setup Node
       uses: actions/setup-node@v4

.github/workflows/theme-update.yml

@@ -8,7 +8,7 @@ jobs:
   update-theme:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4.1.1
+      - uses: actions/checkout@v5
         with:
           ref: main