Use `DjangoJSONEncoder` instead of custom `LazyStringEncoder` #15562

Job	Run time
test-postgres-elasticsearch7 (3.8, Django>=4.2,<4.3, false)	6m 53s
test-mysql (3.9, Django>=4.2,<4.3, false)	17m 15s
test-sqlite (3.10, Django>=4.2,<4.3)	11m 1s
test-postgres (3.8, Django>=4.2,<4.3, false, --parallel)	7m 3s
test-mysql (3.12, Django>=5.0,<5.1, false, --parallel, mysql:8.1)	13m 53s
test-postgres (3.11, Django>=5.0,<5.1, false, emailuser, --parallel)	7m 36s
test-postgres (3.12, Django>=5.0,<5.1, postgres:15, notz, false, --parallel)	9m 37s
test-sqlite-elasticsearch8 (3.10, Django>=5.0,<5.1, emailuser)	10m 52s
test-postgres (3.10, git+https://github.com/django/django.git@stable/5.0.x#egg=Django, true)	15m 47s
test-sqlite-opensearch2 (3.9, Django>=4.2,<4.3, false)	5m 21s
test-postgres (3.10, git+https://github.com/django/django.git@main#egg=Django, true, postgres:lat...	8m 13s
coverage	55s
	1h 54m 26s

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