chore(ci): bump actions/checkout to v6 (#34)

Bump all actions/checkout references to @v6 (org target). v4 runs on a
node runtime version that is being deprecated; v6 is the verified org
standard alongside configure-aws-credentials@v6.

Ref: engineering-handbook cicd.md (workflow standardization).

.github/workflows/cd-cdk.yaml

@@ -53,7 +53,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 30
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: docker/setup-qemu-action@v3
         if: ${{ inputs.enable-qemu }}

.github/workflows/cd-mobile-ios.yaml

@@ -60,7 +60,7 @@ jobs:
       run:
         working-directory: ${{ inputs.working-directory }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: aws-actions/configure-aws-credentials@v4
         with:

.github/workflows/cd-sam.yaml

@@ -40,7 +40,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 15
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: actions/setup-python@v5
         with:

.github/workflows/ci-dotnet.yaml

@@ -28,7 +28,7 @@ jobs:
       run:
         working-directory: ${{ inputs.working-directory }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: actions/setup-dotnet@v5
         with:

.github/workflows/ci-python-sam.yaml

@@ -49,7 +49,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: actions/setup-python@v5
         with:

.github/workflows/ci-typescript-cdk.yaml

@@ -61,7 +61,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 30
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: docker/setup-qemu-action@v3
         if: ${{ inputs.enable-qemu }}

.github/workflows/compliance-audit.yaml

@@ -57,13 +57,13 @@ jobs:
           repositories: ${{ matrix.repo }},engineering-handbook
 
       - name: Checkout repo
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           repository: Sea-Haven-Industries/${{ matrix.repo }}
           token: ${{ steps.app-token.outputs.token }}
 
       - name: Checkout engineering handbook
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           repository: Sea-Haven-Industries/engineering-handbook
           token: ${{ steps.app-token.outputs.token }}