Bump actions/checkout from 2 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

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

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

.github/workflows/crystal.yml

@@ -12,7 +12,7 @@ jobs:
     container:
       image: crystallang/crystal
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Install dependencies
         run: shards install
       - name: Check format
@@ -22,7 +22,7 @@ jobs:
     container:
       image: crystallang/crystal
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Install dependencies
         run: shards install
       - name: Check ameba
@@ -32,7 +32,7 @@ jobs:
     container:
       image: crystallang/crystal
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Install dependencies
         run: shards install
       - name: Run tests
@@ -42,7 +42,7 @@ jobs:
     container:
       image: crystallang/crystal:nightly
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Install dependencies
         run: shards install
       - name: Run tests

.github/workflows/documentation.yml

@@ -10,7 +10,7 @@ jobs:
     container:
       image: crystallang/crystal
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Install dependencies
         run: shards install
       - name: Generate documentation