ci: bump actions/checkout to v6 across all workflows

v6 is the current stable release (v6.0.2) and runs on Node.js 24.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pblazej

.github/workflows/ci.yaml

@@ -96,7 +96,7 @@ jobs:
       run:
         shell: bash
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Install LiveKit Server
         run: brew install livekit
@@ -179,7 +179,7 @@ jobs:
     name: Lint
     runs-on: macos-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install SwiftLint
         run: brew install swiftlint
       - name: SwiftLint
@@ -195,7 +195,7 @@ jobs:
     runs-on: macos-15
     steps:
       - name: Checkout Documentation Catalog
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           sparse-checkout: Sources/LiveKit/LiveKit.docc
 
@@ -230,7 +230,7 @@ jobs:
     name: Check Protocol
     runs-on: macos-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           submodules: recursive
 
@@ -260,7 +260,7 @@ jobs:
       contents: read
       pull-requests: write
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.github/workflows/cocoapods-lint.yaml

@@ -24,7 +24,7 @@ jobs:
     timeout-minutes: 30
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Setup CocoaPods
         uses: maxim-lobanov/setup-cocoapods@v1
         with:

.github/workflows/publish-docs.yaml

@@ -29,7 +29,7 @@ jobs:
             artifact_name: symbol-graph-macos
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.event_name == 'release' && github.event.release.tag_name || github.event.inputs.ref || 'main' }}
           fetch-depth: 0
@@ -63,7 +63,7 @@ jobs:
     runs-on: macos-26
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.event_name == 'release' && github.event.release.tag_name || github.event.inputs.ref || 'main' }}
           fetch-depth: 0

.github/workflows/swift-snapshot.yaml

@@ -20,7 +20,7 @@ jobs:
       run:
         shell: bash
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: maxim-lobanov/setup-xcode@v1
         with: