test(gax): remove resolveResponsePayload tests duplicated by safeJsonStringify tests

resolveResponsePayload passes non-string, non-binary payloads to safeJsonStringify, whose own tests cover circular references and BigInt values. Also drop assertions that repeat the JSON path ([]) or combine two existing cases ((null, null)).

Author: shivanee-p

core/packages/gax/test/unit/errorUtil.ts

@@ -1033,8 +1033,8 @@ describe('errorUtil', () => {
         '{"name":"projects/p/secrets/s","labels":{"env":"prod"},"versions":[1,2]}',
       );
       assert.strictEqual(resolveResponsePayload('raw body'), 'raw body');
+      // Empty responses (e.g. google.protobuf.Empty) still have a payload.
       assert.strictEqual(resolveResponsePayload({}), '{}');
-      assert.strictEqual(resolveResponsePayload([]), '[]');
     });
 
     it('prefers the raw response provided for paginated and long-running calls', () => {
@@ -1054,7 +1054,6 @@ describe('errorUtil', () => {
     it('returns undefined when there is no response', () => {
       assert.strictEqual(resolveResponsePayload(undefined), undefined);
       assert.strictEqual(resolveResponsePayload(null), undefined);
-      assert.strictEqual(resolveResponsePayload(null, null), undefined);
     });
 
     it('serializes protobuf messages through their JSON representation', () => {
@@ -1068,15 +1067,6 @@ describe('errorUtil', () => {
       );
     });
 
-    it('handles circular references and BigInt values without throwing', () => {
-      const response: Record<string, unknown> = {size: 10n};
-      response.self = response;
-      assert.strictEqual(
-        resolveResponsePayload(response),
-        '{"size":"10","self":"[Circular]"}',
-      );
-    });
-
     it('encodes binary payloads as base64', () => {
       assert.strictEqual(
         resolveResponsePayload(Buffer.from('hello')),