Update Django dependency lower bound from 3.2 to 4.2 (#162)

* Update Django dependency lower bound from 3.2 to 4.2

The project no longer supports Django < 4.2 (classifiers and CI matrix
both start at 4.2), but the dependency specifier still allowed 3.2+.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Update poetry lockfile

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: mfogel

poetry.lock

@@ -38,7 +38,7 @@ packages = [
 ]
 
 [tool.poetry.dependencies]
-Django = ">=3.2,<6.1"
+Django = ">=4.2,<6.1"
 python = "^3.8"
 "backports.zoneinfo" = { version = "^0.2.1", python = "<3.9" }