test: unskip tests on Windows (#18600)

Remove the command('qall!') from mksession_spec.lua because it prevents
helpers.rmdir() from retrying.

Allow extra trailing spaces when matching terminal lines.

test/functional/ui/output_spec.lua

@@ -14,7 +14,6 @@ local has_powershell = helpers.has_powershell
 local set_shell_powershell = helpers.set_shell_powershell
 
 describe("shell command :!", function()
-  if helpers.pending_win32(pending) then return end
   local screen
   before_each(function()
     clear()