disable core rule "no-unused-vars" (#205)

* disable core rule "no-unused-vars"

Same problem as in ota-meshi/eslint-plugin-yml#204, same fix as in ota-meshi/eslint-plugin-yml#205

example.jsonc
```json
/* global test */
"data"
```
triggers `1:11  error  'test' is defined but never used. Allowed unused vars must match /^_/u  no-unused-vars`

* Create smart-bottles-beam.md

Co-authored-by: Yosuke Ota <[email protected]>

Author: danielrentz

.changeset/smart-bottles-beam.md

@@ -0,0 +1,5 @@
+---
+"eslint-plugin-jsonc": minor
+---
+
+disable `no-unused-vars` in base config

lib/configs/base.ts

@@ -8,6 +8,7 @@ export = {
         // ESLint core rules known to cause problems with JSON.
         strict: "off",
         "no-unused-expressions": "off",
+        "no-unused-vars": "off",
       },
     },
   ],