Backport "Make PC tests more stable" to LTS (#20689)

Backports #18640 to the LTS branch.

PR submitted by the release tooling.
[skip ci]

Author: WojciechMazur

presentation-compiler/test/dotty/tools/pc/tests/completion/CompletionSuite.scala

@@ -715,7 +715,7 @@ class CompletionSuite extends BaseCompletionSuite:
       s"""|object Main {
           |  val Number = "".r
           |  "" match {
-          |    case _: NotImpl@@
+          |    case _: NotImplementedErr@@
           |}
           |""".stripMargin,
       """|NotImplementedError scala