Converted a SimpleTestCase that creates data to TestCase.
Fixed #23954 -- Added special text/varchar PostgreSQL indexes in migrations

Thanks adityagupta104 for the report and Tim Graham for the review.
Removed stray conflict line in 1.7.2 release notes.
Added versionadded annotation for contrib.postgres.
Fixed #23957 -- Started deprecation toward requiring session verification.

Thanks Carl Meyer for review.