Revert "Update actions/checkout action to v6"

.github/workflows/check-nix-format.yml

@@ -19,7 +19,7 @@ jobs:
     name: nixfmt-check
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+      - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
         with:
           fetch-depth: 2
       - name: Calculate changed files

.github/workflows/pr.yml

@@ -10,7 +10,7 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+    - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
     - uses: cachix/install-nix-action@4e002c8ec80594ecd40e759629461e26c8abed15 # v31
       with:
         nix_path: nixpkgs=channel:nixos-unstable

.github/workflows/update.yml

@@ -23,7 +23,7 @@ jobs:
         application_private_key: '${{ secrets.GH_APPLICATION_PRIVATE_KEY }}'
         permissions: "contents:write"
         revoke_token: true
-    - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6
+    - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
     - uses: cachix/install-nix-action@4e002c8ec80594ecd40e759629461e26c8abed15 # v31
       with:
         nix_path: nixpkgs=channel:nixos-unstable