Bump checkout action to v6

Author: kfl

.github/workflows/check-nix.yaml

@@ -5,7 +5,7 @@ jobs:
   nix-flake:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install Nix
         uses: cachix/install-nix-action@v31
@@ -25,7 +25,7 @@ jobs:
   nix-shell:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install Nix
         uses: cachix/install-nix-action@v31

.github/workflows/check-types.yaml

@@ -5,7 +5,7 @@ jobs:
   python-check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install uv
         uses: astral-sh/setup-uv@v7