chore: Add dependabot for CI (#63)

Author: samuelburnham

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      actions-dependencies:
+        patterns:
+          - "*"

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     name: Lean Build
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: leanprover/lean-action@v1
         with:
           build-args: "--wfail"
@@ -24,7 +24,7 @@ jobs:
     name: Nix Flake Check
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - uses: cachix/install-nix-action@v31
         with:
           nix_path: nixpkgs=channel:nixos-unstable