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/ex_cmds/mksession_spec.lua

@@ -14,7 +14,6 @@ local rmdir = helpers.rmdir
 local file_prefix = 'Xtest-functional-ex_cmds-mksession_spec'
 
 describe(':mksession', function()
-  if helpers.pending_win32(pending) then return end
   local session_file = file_prefix .. '.vim'
   local tab_dir = file_prefix .. '.d'
 
@@ -114,6 +113,5 @@ describe(':mksession', function()
 
     local expected_cwd = cwd_dir..'/'..tab_dir
     matches('^term://'..pesc(expected_cwd)..'//%d+:', funcs.expand('%'))
-    command('qall!')
   end)
 end)