MM-29487: Fix racy TestMuteCommandSpecificChannel (#16290)

The code was doing `go fakeApp.UpdateProductNotices()`
due to which the Store object was accessed in a racy manner
when it was reset if the localcachelayer flag was set.

We fix this by using the StoreOverride functionality
to pre-define what store to use while initializing the server
itself so that there isn't a need to reset the store _after_
the server is set.

We also apply the same fix in the app and api4 layers too
to prevent similar things from happening there.

https://mattermost.atlassian.net/browse/MM-29487

```release-note
NONE
```

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/apitestlib.go

@@ -99,16 +99,19 @@ func setupTestHelper(dbStore store.Store, searchEngine *searchengine.Broker, ent
 
 	var options []app.Option
 	options = append(options, app.ConfigStore(configStore))
-	options = append(options, app.StoreOverride(dbStore))
+	if includeCache {
+		// Adds the cache layer to the test store
+		options = append(options, app.StoreOverride(func(s *app.Server) store.Store {
+			return localcachelayer.NewLocalCacheLayer(dbStore, s.Metrics, s.Cluster, s.CacheProvider)
+		}))
+	} else {
+		options = append(options, app.StoreOverride(dbStore))
+	}
 
 	s, err := app.NewServer(options...)
 	if err != nil {
 		panic(err)
 	}
-	if includeCache {
-		// Adds the cache layer to the test store
-		s.Store = localcachelayer.NewLocalCacheLayer(s.Store, s.Metrics, s.Cluster, s.CacheProvider)
-	}
 
 	th := &TestHelper{
 		App:               app.New(app.ServerConnector(s)),

app/helper_test.go

@@ -65,7 +65,14 @@ func setupTestHelper(dbStore store.Store, enterprise bool, includeCacheLayer boo
 
 	var options []Option
 	options = append(options, ConfigStore(configStore))
-	options = append(options, StoreOverride(dbStore))
+	if includeCacheLayer {
+		// Adds the cache layer to the test store
+		options = append(options, StoreOverride(func(s *Server) store.Store {
+			return localcachelayer.NewLocalCacheLayer(dbStore, s.Metrics, s.Cluster, s.CacheProvider)
+		}))
+	} else {
+		options = append(options, StoreOverride(dbStore))
+	}
 	options = append(options, SetLogger(mlog.NewTestingLogger(tb, buffer)))
 
 	s, err := NewServer(options...)
@@ -73,11 +80,6 @@ func setupTestHelper(dbStore store.Store, enterprise bool, includeCacheLayer boo
 		panic(err)
 	}
 
-	if includeCacheLayer {
-		// Adds the cache layer to the test store
-		s.Store = localcachelayer.NewLocalCacheLayer(s.Store, s.Metrics, s.Cluster, s.CacheProvider)
-	}
-
 	th := &TestHelper{
 		App:               New(ServerConnector(s)),
 		Server:            s,

app/slashcommands/helper_test.go

@@ -60,7 +60,13 @@ func setupTestHelper(dbStore store.Store, enterprise bool, includeCacheLayer boo
 
 	var options []app.Option
 	options = append(options, app.ConfigStore(memoryStore))
-	options = append(options, app.StoreOverride(dbStore))
+	if includeCacheLayer {
+		options = append(options, app.StoreOverride(func(s *app.Server) store.Store {
+			return localcachelayer.NewLocalCacheLayer(dbStore, s.Metrics, s.Cluster, s.CacheProvider)
+		}))
+	} else {
+		options = append(options, app.StoreOverride(dbStore))
+	}
 	options = append(options, app.SetLogger(mlog.NewTestingLogger(tb, buffer)))
 
 	s, err := app.NewServer(options...)
@@ -68,11 +74,6 @@ func setupTestHelper(dbStore store.Store, enterprise bool, includeCacheLayer boo
 		panic(err)
 	}
 
-	if includeCacheLayer {
-		// Adds the cache layer to the test store
-		s.Store = localcachelayer.NewLocalCacheLayer(s.Store, s.Metrics, s.Cluster, s.CacheProvider)
-	}
-
 	th := &TestHelper{
 		App:               app.New(app.ServerConnector(s)),
 		Server:            s,