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/terminal/highlight_spec.lua

@@ -117,7 +117,6 @@ describe(':terminal highlight', function()
 end)
 
 it(':terminal highlight has lower precedence than editor #9964', function()
-  if helpers.pending_win32(pending) then return end
   clear()
   local screen = Screen.new(30, 4)
   screen:set_default_attr_ids({