Bump actions/checkout from 2 to 5

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 5.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...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] <[email protected]>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v5
     - uses: jiro4989/setup-nim-action@v2
       with:
         nim-version: ${{ matrix.nim-version }}

.github/workflows/docs.yml

@@ -11,7 +11,7 @@ jobs:
   docs:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v5
       - uses: jiro4989/setup-nim-action@v1
         with:
           nim-version: ${{ env.nim-version }}