Do not use toHaveLength for objects

Mocha supported `.to.have.length` for objects, but Jest only allows
`toHaveLength` on objects which have a length property (such as arrays).

Author: koesie10

extensions/ql-vscode/src/vscode-tests/cli-integration/legacy-query.test.ts

@@ -250,7 +250,7 @@ describeWithCodeQL()("using the legacy query server", () => {
 
     it(`should have correct results for query ${queryName}`, async () => {
       await parsedResults.done();
-      expect(actualResultSets!).not.toHaveLength(0);
+      expect(actualResultSets).not.toEqual({});
       expect(Object.keys(actualResultSets!).sort()).toEqual(
         Object.keys(queryTestCase.expectedResultSets).sort(),
       );