Bump actions/checkout from 6 to 6.0.3 (django#2677)

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 6.0.3.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v6...v6.0.3)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: 6.0.3
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

.github/workflows/docker-publish.yml

@@ -17,7 +17,7 @@ jobs:
 
         steps:
             - name: Checkout repository
-              uses: actions/checkout@v6
+              uses: actions/checkout@v6.0.3
 
             - name: Log in to the Container registry
               uses: docker/login-action@v4

.github/workflows/docker-test-build.yml

@@ -23,7 +23,7 @@ jobs:
         # steps taken (and trimmed) from docker-publish.yml
         steps:
             - name: Checkout repository
-              uses: actions/checkout@v6
+              uses: actions/checkout@v6.0.3
 
             - if: matrix.req_file != 'tests.txt'
               name: Test docker image build (${{ matrix.req_file }})

.github/workflows/prek.yml

@@ -9,5 +9,5 @@ jobs:
     prek:
         runs-on: ubuntu-24.04
         steps:
-            - uses: actions/checkout@v6
+            - uses: actions/checkout@v6.0.3
             - uses: j178/prek-action@v1.1.1

.github/workflows/tests.yml

@@ -28,7 +28,7 @@ jobs:
                     - 5432:5432
 
         steps:
-            - uses: actions/checkout@v6
+            - uses: actions/checkout@v6.0.3
             - name: Set up Python
               uses: actions/setup-python@v6
               with: