Prepare UI tests for Rust 1.51 & new CI image (#8474)

* Prepare UI tests for Rust 1.51 & new CI image

* another stderr to be fixed

Co-authored-by: Denis P <denis.pisarev@parity.io>

substrate/frame/support/test/tests/construct_runtime_ui/missing_system_module.stderr

@@ -1,7 +1,6 @@
 error: `System` pallet declaration is missing. Please add this line: `System: frame_system::{Pallet, Call, Storage, Config, Event<T>},`
  --> $DIR/missing_system_module.rs:8:2
   |
-8 |       {
-  |  _____^
+8 | /     {
 9 | |     }
   | |_____^