Fail vs. fatal on store startup (#24170)

If the store fails to initialize (e.g. run a migration), it would `log.Fatal` and then `os.Exit`. Unfortunately, this trips up `TestMain`, which happily keeps running tests, now guaranteed to fail.

Avoid this by instead returning an error from the store initialization, handling appropriately at the layer above.

server/channels/store/localcachelayer/layer_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/mattermost/mattermost/server/v8/channels/store"
 	"github.com/mattermost/mattermost/server/v8/channels/store/sqlstore"
 	"github.com/mattermost/mattermost/server/v8/channels/store/storetest"
+	"golang.org/x/sync/errgroup"
 )
 
 type storeType struct {
@@ -91,23 +92,29 @@ func initStores() {
 			panic(err)
 		}
 	}()
-	var wg sync.WaitGroup
+	var eg errgroup.Group
 	for _, st := range storeTypes {
 		st := st
-		wg.Add(1)
-		go func() {
+		eg.Go(func() error {
 			var err error
-			defer wg.Done()
-			st.SqlStore = sqlstore.New(*st.SqlSettings, nil)
+
+			st.SqlStore, err = sqlstore.New(*st.SqlSettings, nil)
+			if err != nil {
+				return err
+			}
 			st.Store, err = NewLocalCacheLayer(st.SqlStore, nil, nil, getMockCacheProvider())
 			if err != nil {
-				panic(err)
+				return err
 			}
 			st.Store.DropAllTables()
 			st.Store.MarkSystemRanUnitTests()
-		}()
+
+			return nil
+		})
+	}
+	if err := eg.Wait(); err != nil {
+		panic(err)
 	}
-	wg.Wait()
 }
 
 var tearDownStoresOnce sync.Once