Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v6)

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

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

Author: dependabot[bot]

.github/workflows/dev-containers.yml

@@ -13,7 +13,7 @@ jobs:
     name: CLI
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - uses: actions/setup-node@v5
       with:
         node-version: '18.x'
@@ -62,7 +62,7 @@ jobs:
         ]
     steps:
     - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Setup Node.js
       uses: actions/setup-node@v5
       with:
@@ -95,7 +95,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Setup Node.js
       uses: actions/setup-node@v5
       with:

.github/workflows/publish-dev-containers.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Setup Node.js
       uses: actions/setup-node@v5
       with:

.github/workflows/test-docker-v29.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: actions/setup-node@v5
       with:

.github/workflows/test-plan-item-validator.yml

@@ -9,7 +9,7 @@ jobs:
     steps:
       - name: Checkout Actions
         if: contains(github.event.issue.labels.*.name, 'testplan-item') || contains(github.event.issue.labels.*.name, 'invalid-testplan-item')
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           repository: 'microsoft/vscode-github-triage-actions'
           ref: stable

.github/workflows/test-windows.yml

@@ -46,7 +46,7 @@ jobs:
         ]
     steps:
     - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Setup Node.js
       uses: actions/setup-node@v5
       with: