generate_expected_output.py: placate FutureWarning from python

Regexes have long specified that a [ as the first character inside a
[...] is just a literal [, but apparently we need to escape it now, to
avoid a "nested set" FutureWarning.

Change-Id: I76a48c9aafb0684a1d6b0d5284fe9852c9ea0e43
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Samuel Gaist <samuel.gaist@idiap.ch>

tests/auto/testlib/selftests/generate_expected_output.py

@@ -132,7 +132,7 @@ class Cleaner (object):
         # Add path to specific sources and to tst_*.cpp if missing (for in-source builds):
         patterns += ((r'(^|[^/])\b(qtestcase.cpp)\b', r'\1qtbase/src/testlib/\2'),
                      # Add more special cases here, if they show up !
-                     (r'([[" ])\.\./(counting/tst_counting.cpp)\b',
+                     (r'([\[" ])\.\./(counting/tst_counting.cpp)\b',
                       r'\1' + os.path.sep.join(hereNames + (r'\2',))),
                      # The common pattern:
                      (r'(^|[^/])\b(tst_)?([a-z]+\d*)\.cpp\b',