fix(releases): Add missing builds mock and prevent tab flicker on refetch

Add MockApiClient response for /builds/ endpoint in release list tests.
Use keepPreviousData to prevent the mobile builds tab from flickering
when query keys change during filter updates.

Author: NicoHinderling

static/app/views/releases/list/index.spec.tsx

@@ -100,6 +100,10 @@ describe('ReleasesList', () => {
       method: 'POST',
       body: {attributes: {}},
     });
+    MockApiClient.addMockResponse({
+      url: `/organizations/${organization.slug}/builds/`,
+      body: [],
+    });
   });
 
   afterEach(() => {

static/app/views/releases/list/index.tsx

@@ -1,7 +1,7 @@
 import {Fragment, useCallback, useEffect, useMemo} from 'react';
 import {forceCheck} from 'react-lazyload';
 import styled from '@emotion/styled';
-import {useQuery} from '@tanstack/react-query';
+import {keepPreviousData, useQuery} from '@tanstack/react-query';
 
 import {FeatureBadge} from '@sentry/scraps/badge';
 import {Flex, Stack} from '@sentry/scraps/layout';
@@ -251,6 +251,7 @@ export default function ReleasesList() {
     }),
     staleTime: 60_000,
     enabled: !!hasPreprodFeature,
+    placeholderData: keepPreviousData,
   });
 
   // When "All Projects" is selected (represented by [-1]), check all accessible projects