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/api/buffer_updates_spec.lua

@@ -828,7 +828,6 @@ describe('API: buffer events:', function()
   end
 
   it('when :terminal lines change', function()
-    if helpers.pending_win32(pending) then return end
     local buffer_lines = {}
     local expected_lines = {}
     command('terminal "'..nvim_prog..'" -u NONE -i NONE -n -c "set shortmess+=A"')