fix: upgrade actions/checkout to v4

Author: develop7

.github/workflows/debian.yml

@@ -36,7 +36,7 @@ jobs:
           - ghc: '9.8.1'
             ghc_minor: '9.8'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: build + smoke test [${{ matrix.ghc }}]
         uses: nick-invision/retry@v2
         with:
@@ -46,7 +46,7 @@ jobs:
             docker build --pull \
               -t haskell:${{ matrix.ghc }}-${{ matrix.deb }} \
               ${{ matrix.ghc_minor }}/${{ matrix.deb }}
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
         with:
           repository: AlistairB/official-images
           ref: haskell-cabal-test-change

.github/workflows/lint.yml

@@ -12,7 +12,7 @@ jobs:
   hadolint:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - uses: hadolint/hadolint-action@v1.6.0
       with:
         recursive: true