Migrations containing RunPython operations cannot be reversed regardless of reverse_code

[andrewsg]

Migrations including RunPython cannot be reversed, regardless of whether reverse_code is supplied to RunPython. Code appears to be in place to make the reverse operation function if reverse_code is supplied, but the "reversible" attribute on the RunPython class is set to False.

RunSQL is analogous to RunPython and solves this problem by making reversible a property that returns True if reverse_sql is supplied to that constructor, so presumably the same would work for RunPython.

[andrewsg]

Fix supplied in PR: ​https://github.com/django/django/pull/2329

[Baptiste Mispelon <bmispelon@…>]

In 202bf69c2f69d9ee20ac3fd409116a8946dc0784:

Fixed #22095 -- Enabled backward migrations for RunPython operations

Added reversible property to RunPython so that migrations will not
refuse to reverse migrations including RunPython operations, so long as
reverse_code is set in the RunPython constructor. Included tests to
check the reversible property on RunPython and the similar RunSQL.