pgsql: Reset standard_conforming_strings in strings test

Reset standard_conforming_strings in strings test

After some tests relating to standard_conforming_strings behavior, the
value was not reset to the default value. Therefore, the rest of the
tests in that file ran with the nondefault setting, which affected the
results of some tests. For clarity, reset the value and run the rest
of the tests with the default setting again.

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/ebedd0c78fc51c293abe56e99a18c67af14da0c9

Modified Files
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src/test/regress/expected/strings.out | 3 ++-
src/test/regress/sql/strings.sql | 2 ++
2 files changed, 4 insertions(+), 1 deletion(-)