Missing function call `()` leads to:

TypeError: descriptor '__init__' of 'super' object needs an argument

Regression in b209518089131c6b4afd18b1d9c320ba3521c5ab.

Thanks David Sanders for the report.

While deferring many-to-many and GFK has no effect, the previous
implementation of QuerySet.defer() ignore them instead of crashing.

Regression in b3db6c8dcb5145f7d45eff517bcd96460475c879.

Thanks Paco Martínez for the report.

Regression in 5c23d9f0c32f166c81ecb6f3f01d5077a6084318.

Special thanks to Hannes Ljungberg for finding multiple implementation
gaps.

Thanks also to Simon Charette, Adam Johnson, and Mariusz Felisiak for
reviews.

Proper escaping of % in string literals used when defining constaints
was attempted (a8b3f96f6) by overriding quote_value of Postgres and
Oracle schema editor. The same approach was used when adding support for
constraints to the MySQL/MariaDB backend (1fc2c70).

Later on it was discovered that this approach was not appropriate and
that a preferable one was to pass params=None when executing the
constraint creation DDL to avoid any form of interpolation in the first
place (42e8cf47).

When the second patch was applied the corrective of the first were not
removed which caused % literals to be unnecessary doubled. This flew
under the radar because the existings test were crafted in a way that
consecutive %% didn't catch regressions.

This commit introduces an extra test for __exact lookups which
highlights more adequately % doubling problems but also adjust a
previous __endswith test to cover % doubling problems (%\% -> %%\%%).

Thanks Thomas Kolar for the report.

Refs #32369, #30408, #30593.

This ensures that constraint violations are tested in isolation from
each other as an IntegrityError only ensures a least one constraint is
violated.

For example, the assertion added in 42e8cf4 break both the
name_constraint_rhs and the rebate_constraint constraints and thus
doesn't constitute a proper regression test. Refs #32369.