Mm 16623 fix all initialism errors in channels/app and channels/api4 and /store dir (#25787)

server/channels/store/searchtest/testlib.go

@@ -13,7 +13,7 @@ import (
 
 const (
 	EngineAll           = "all"
-	EngineMySql         = "mysql"
+	EngineMySQL         = "mysql"
 	EnginePostgres      = "postgres"
 	EngineElasticSearch = "elasticsearch"
 	EngineBleve         = "bleve"