Backport "Nopos-warn in vulpix & Move warn tests form tests/neg to tests/warn: Batch 1" to LTS (#20821)

Backports #19242 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

Author: WojciechMazur

tests/neg-deep-subtype/i3324.scala

@@ -0,0 +1,5 @@
+-- Error: tests/neg/i11225b.scala:6:26 ---------------------------------------------------------------------------------
+6 |  private var cached: A = _ // error
+  |                          ^
+  |                          `= _` has been deprecated; use `= uninitialized` instead.
+  |                          `uninitialized` can be imported with `scala.compiletime.uninitialized`.

tests/neg/i10247.scala

@@ -10,3 +10,4 @@ class Memo[A](x: => A):
       known = true
       cached = x
     cached
+

tests/neg/i10930.scala

@@ -1,12 +1,11 @@
 -- [E081] Type Error: tests/neg/i19334.scala:6:4 -----------------------------------------------------------------------
 6 |  f(_) // error was OOM formatting TypeVar(TypeParamRef(T)) when offering explanations
   |    ^
-  |    Missing parameter type
+  |    Could not infer type for parameter _$1 of anonymous function
   |
-  |    I could not infer the type of the parameter _$1
-  |    in expanded function:
-  |      _$1 => f(_$1)
-  |    Expected type for the whole anonymous function:
-  |      T
+  |    In expanded function:
+  |    _$1 => f(_$1)
+  |
+  |    Expected type for the whole anonymous function: T
   |
   |    where:    T is a type variable