Nightly Dotty workflow of 2022-04-28 failed

[github-actions]

See https://github.com/lampepfl/dotty/actions/runs/2236991940

[griggt]

Ah, our old friend the Windows directory separator.

In test_windows_full:

Error:  Test dotty.tools.languageserver.HoverTest.topLevel failed: java.lang.AssertionError: 
Error:  
Error:  // project299\Source0.scala in project project299
Error:  package hello
Error:  val x: Int = 1
Error:  val y = this.x
Error:  
Error:  while executing action: CodeHover([start=(m1,line=2,char=8), end=(m2,line=2,char=12)], Some(```scala
Error:  (hello.Source0$package : hello.Source0$package.type)
Error:  ```))
Error:  
Error:            expected:<```scala
Error:  ([hello.Source0$package : hello.Source0$package.type])
Error:  ```> but was:<```scala
Error:  ([
Error:    hello.C:\actions-runner2\_work\dotty\dotty\out\ide-tests\src\project299\Source0$package
Error:   : 
Error:    hello.
Error:      C:\actions-runner2\_work\dotty\dotty\out\ide-tests\src\project299\Source0$package
Error:    .type
Error:  ])
Error:  ```>, took 0.047 sec

https://github.com/lampepfl/dotty/blob/b1f00a78eba1eb22c4b2defaa88acc6e025ef59a/compiler/src/dotty/tools/io/VirtualFile.scala#L107-L109