chore(deps): 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/ci.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Set up JDK 17
         uses: actions/setup-java@v4
@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Set up JDK 17
         uses: actions/setup-java@v4

.github/workflows/conformance.yml

@@ -11,7 +11,7 @@ jobs:
     name: Server Conformance
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up JDK 17
         uses: actions/setup-java@v4
@@ -41,7 +41,7 @@ jobs:
       matrix:
         scenario: [initialize, tools_call, elicitation-sep1034-client-defaults, sse-retry]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up JDK 17
         uses: actions/setup-java@v4
@@ -82,7 +82,7 @@ jobs:
         - auth/token-endpoint-auth-none
         - auth/pre-registration
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up JDK 17
         uses: actions/setup-java@v4

.github/workflows/docs.yml

@@ -19,7 +19,7 @@ jobs:
   deploy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.github/workflows/maven-central-release.yml

@@ -7,7 +7,7 @@ jobs:
   publish:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Java
         uses: actions/setup-java@v4

.github/workflows/publish-snapshot.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Set up JDK 17
         uses: actions/setup-java@v4