ci: update flake inputs with dependabot; add cooldown to Rust deps

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: Iac735278f32f323106314eb9d94159f06a6a6964

.github/dependabot.yaml

@@ -1,13 +1,23 @@
 version: 2
 updates:
-  # Update Cargo deps
-  - package-ecosystem: cargo
-    directory: "/"
-    schedule:
-      interval: "weekly"
-
   # Update used workflows
   - package-ecosystem: github-actions
     directory: "/"
     schedule:
       interval: daily
+
+  # Update Cargo deps
+  - package-ecosystem: cargo
+    directory: "/"
+    cooldown:
+      default-days: 7
+    schedule:
+      interval: "weekly"
+
+  # Update Nixpkgs & Crane
+  - package-ecosystem: nix
+    directory: "/"
+    cooldown:
+      default-days: 7
+    schedule:
+      interval: daily