Bump actions/checkout from 5 to 6 in the dependencies group (#186)

Bumps the dependencies group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `actions/checkout` from 5 to 6
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: dependencies
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/api-breakage.yml

@@ -10,7 +10,7 @@ jobs:
       image: swift:5.9
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         fetch-depth: 0
     # https://github.com/actions/checkout/issues/766

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
     timeout-minutes: 15
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Install and run Mosquitto
       run: |
         brew install mosquitto
@@ -44,7 +44,7 @@ jobs:
     timeout-minutes: 15
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Xcodebuild
       run: |
         xcodebuild build -scheme mqtt-nio -destination 'platform=iOS Simulator,name=iPhone 16'
@@ -77,7 +77,7 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Restart Mosquitto
       # The mosquitto service container is started *before* mqtt-nio is checked
       # out. Restarting the container after the checkout step is needed for the

.github/workflows/gen-docs.yml

@@ -12,7 +12,7 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - name: Install Dependencies

.github/workflows/validate.yml

@@ -12,7 +12,7 @@ jobs:
     timeout-minutes: 15
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         fetch-depth: 1
     - name: run script