Fix flaky migrations tests (elastic#111365)

# Conflicts:
#	src/core/server/saved_objects/migrationsv2/integration_tests/batch_size_bytes.test.ts

src/core/server/saved_objects/migrationsv2/test_helpers/retry.test.ts

@@ -52,6 +52,8 @@ describe('retry', () => {
       },
       { retryAttempts: 3, retryDelayMs: 100 }
     );
-    expect(Date.now() - now).toBeGreaterThanOrEqual(200);
+    // Would expect it to take 200ms but seems like timing inaccuracies
+    // sometimes causes the duration to be measured as 199ms
+    expect(Date.now() - now).toBeGreaterThanOrEqual(199);
   });
 });