Bump actions/checkout from 5 to 6 (#3974)

Bumps [actions/checkout](https://github.com/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
...

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

Author: dependabot[bot]

.github/workflows/build_artifacts.yml

@@ -26,7 +26,7 @@ jobs:
             solution: MaterialDesignToolkit.Full.sln
 
         steps:
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
 
             - name: Setup .NET
               uses: actions/setup-dotnet@v5

.github/workflows/control_styles.yml

@@ -10,7 +10,7 @@ jobs:
         runs-on: ubuntu-latest
 
         steps:
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
             - name: Generate Control Styles Markdown
               run: build/GenerateThemesWikiMarkdown.ps1
               shell: pwsh

.github/workflows/icon_update.yml

@@ -20,7 +20,7 @@ jobs:
         runs-on: windows-latest
 
         steps:
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
 
             - name: Run Icon Generation
               run: dotnet run -c Release -- icons

.github/workflows/release.yml

@@ -85,7 +85,7 @@ jobs:
         name: Get Icon Changes
 
         steps:
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
               with:
                   fetch-depth: 0
 
@@ -156,7 +156,7 @@ jobs:
 
         steps:
             - name: Checkout Wiki Repo
-              uses: actions/checkout@v5
+              uses: actions/checkout@v6
               with:
                   repository: ${{ github.repository }}.wiki
 
@@ -254,7 +254,7 @@ jobs:
             # Doing a checkout, until this issue is resolved.
             # https://github.com/valeriobelli/gh-milestone/issues/15
             # As of version 2.1.0 the -R doesn't appear to output valid json when filtering. So still using the checkout.
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
 
             - name: Close Milestone
               run: |
@@ -274,7 +274,7 @@ jobs:
 
         steps:
             # Checkout is needed so that we can update the get_versions.yml file
-            - uses: actions/checkout@v5
+            - uses: actions/checkout@v6
 
             - name: Increment Version Numbers
               run: |