Update actions/checkout from v4.1.1 to v6.0.2 (#27)

Node 20 reaches EOL in April 2026 and GitHub will force Node 24
after June 2, 2026. v6 already uses Node 24 natively.

Author: SeanTAllen

.github/workflows/lint-action-workflows.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4.1.1
+        uses: actions/checkout@v6.0.2
       - name: Check workflow files
         uses: docker://ghcr.io/ponylang/shared-docker-ci-actionlint:20260311
         with:

.github/workflows/pr.yml

@@ -14,15 +14,15 @@ jobs:
     name: Lint entrypoint.py
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4.1.1
+      - uses: actions/checkout@v6.0.2
       - name: pylint
         run: make pylint
 
   superlinter:
     name: Lint bash, docker, markdown, and yaml
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4.1.1
+      - uses: actions/checkout@v6.0.2
       - name: Lint codebase
         uses: docker://github/super-linter:v3.8.3
         env:
@@ -37,14 +37,14 @@ jobs:
     name: Validate release image builds
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4.1.1
+      - uses: actions/checkout@v6.0.2
       - name: Docker build
         run: make build-release
 
   validate-nightly-image-builds:
     name: Validate nightly image builds
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4.1.1
+      - uses: actions/checkout@v6.0.2
       - name: Docker build
         run: make build-nightly

.github/workflows/update-nightly-image.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source
-        uses: actions/checkout@v4.1.1
+        uses: actions/checkout@v6.0.2
       - name: Login to GitHub Container Registry
         # v2.2.0
         uses: docker/login-action@5139682d94efc37792e6b54386b5b470a68a4737

.github/workflows/update-release-image.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source
-        uses: actions/checkout@v4.1.1
+        uses: actions/checkout@v6.0.2
       - name: Login to GitHub Container Registry
         # v2.2.0
         uses: docker/login-action@5139682d94efc37792e6b54386b5b470a68a4737
@@ -54,7 +54,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source
-        uses: actions/checkout@v4.1.1
+        uses: actions/checkout@v6.0.2
       - name: Login to GitHub Container Registry
         # v2.2.0
         uses: docker/login-action@5139682d94efc37792e6b54386b5b470a68a4737