Fixed #23609 -- Fixed IntegrityError that prevented altering a NULL column into a NOT NULL one due to existing rows

Thanks to Simon Charette, Loic Bistuer and Tim Graham for the review.
Updated release notes following backport of a407b84. Refs #23365.
Skip another test if sqlparse is not available

Refs #23426
Fixed #23627 -- Allowed register_lookup to work as a decorator.
Fixed #23612 -- Normalized fixuture paths to allow referencing relative paths on Windows.
Avoided requiring sqlparse for a test.

Refs #23426. Thanks Markus Holtermann for the suggestion.
Converted GIS lookups to use the new Lookup API

Thanks Tim Graham, Anssi Kääriäinen and Marc Tamlyn for the
reviews.
Converted GIS lookups for Oracle