"The fix" is to tell Mercurial that the test files are binary.
Windows developers: to get the correct line endings in your checkout,
delete Lib\test\xmltestdata, and then "hg revert" that directory.
Why the Windows buildbots didn't fail test_sax remains a mystery :-(
Lib/test/decimaltestdata/*.decTest = BIN
Lib/test/sndhdrdata/sndhdr.* = BIN
Lib/test/test_email/data/msg_26.txt = BIN
+Lib/test/xmltestdata/* = BIN
Lib/venv/scripts/nt/* = BIN