chore: fix json schema URL

Our TOML linting currently fails with:

```text
Error: failed to fetch catalog: https://json.schemastore.org/api/json/catalog.json, reason: unexpected status: 503
```

Setting the store URL to the actual new location helps.

Also see SchemaStore/schemastore#5106 .

Author: crepererum

tombi.toml

@@ -1,2 +1,9 @@
 [files]
 exclude = [".jj/**/*.toml", "target/**/*.toml"]
+
+[schema]
+catalog = {
+  paths = [
+    "https://www.schemastore.org/api/json/catalog.json",
+  ],
+}