Adjust regex for test with opening parenthesis in character classes
As written, the test was throwing an error because of an unbalanced
parenthesis. The regex used in the test is adjusted to not fail and to
test the case of an opening parenthesis in a character class after some
nested square brackets.
Oversight in
d46911e584d4.
Discussion: https://postgr.es/m/
16ab039d1af455652bdf4173402ddda145f2c73b.camel@cybertec.at