Fixed documentation of GeoModelAdmin.openlayers_url
Fixed typo in docs/ref/applications.txt.
Cleaned up a note in docs/topics/db/sql.txt.
Fixed #23958 -- Rewrote filter tests as unit tests.
Refs #23890 -- Restored silencing of numpy DeprecationWarnings in template tests.
Fixed #23965 -- Mentioned that FieldFile inherits from File
Refs #23947 -- Isolated a mail test.
Refs #23947 -- Fixed introspection test that had a side effect.
Refs #23947 -- Isolated some cache tests.

Thanks Diego Guimarãesi and Florian Apolloner.
Updated obsolete comment.
Moved misplaced comment.
Refs #23947 -- Worked around a bug in Python that prevents deprecation warnings from appearing in tests.