Error when _lzma extension is missing:

test test_zoneinfo crashed -- Traceback (most recent call last):                                                                                                                             
  File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 272, in _runtest_inner
    refleak = _runtest_inner2(ns, test_name)                                                  
  File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 223, in _runtest_inner2                                                                                          
    the_module = importlib.import_module(abstest)                                                                                                                                            
  File "/home/vstinner/python/master/Lib/importlib/__init__.py", line 126, in import_module                                                                                                  
    return _bootstrap._gcd_import(name[level:], package, level)                                                                                                                              
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import                                                                                                                            
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked                                                                                                                 
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked                                                                                                                          
  File "<frozen importlib._bootstrap_external>", line 790, in exec_module                                                                                                                    
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed              
  File "/home/vstinner/python/master/Lib/test/test_zoneinfo/__init__.py", line 1, in <module>                                                                                                
    from .test_zoneinfo import *                                                                                                                                                             
  File "/home/vstinner/python/master/Lib/test/test_zoneinfo/test_zoneinfo.py", line 9, in <module>                                
    import lzma                                                                                                                                                                              
  File "/home/vstinner/python/master/Lib/lzma.py", line 27, in <module>                                                                                                                      
    from _lzma import *                                                                                                                                                                      
ModuleNotFoundError: No module named '_lzma'


The minimum fix is to skip test_zoneinfo is lzma is missing. For example, replace "import lzma" with "lzma = support.import_helper.import_module('lzma')".