Add default pre_commit.

tests/parsing/defaults.toml

@@ -0,0 +1 @@
+[[pre_commit]]

tests/snapshots/parsing__defaults.snap

@@ -6,5 +6,14 @@ Config {
     general: General {
         directory: "hooks",
     },
-    pre_commit: [],
+    pre_commit: [
+        PreCommit {
+            name: None,
+            on_failure: Stop,
+            task: Task {
+                command: None,
+                script: None,
+            },
+        },
+    ],
 }