Fix lint issue in rate metric code

Author: ChinYing-Li

glean/src/core/metrics/types/rate.ts

@@ -7,7 +7,8 @@ import { MetricType } from "../index.js";
 import { Context } from "../../context.js";
 import { Metric } from "../metric.js";
 import { testOnly } from "../../utils.js";
-import { isNumber, isObject, JSONValue } from "../../utils.js";
+import { isNumber, isObject } from "../../utils.js";
+import type { JSONValue } from "../../utils.js";
 import { ErrorType } from "../../error/error_type.js";
 
 const LOG_TAG = "core.metrics.RateMetricType";

glean/tests/unit/core/metrics/rate.spec.ts

@@ -43,5 +43,5 @@ describe("RateMetric", function() {
     metric.add_to_denominator(7);
 
     assert.deepStrictEqual(await metric.testGetValue("aPing"), {numerator: 22, denominator: 7});
- });
+  });
 });