Add tests for JSON Schema 2020-12 field preservation (SEP-1613) #3505

Job	Run time
checks / pre-commit	31s
checks / readme-snippets	9s
checks / test (3.10, lowest-direct, ubuntu-latest)	47s
checks / test (3.10, highest, windows-latest)	1m 58s
checks / test (3.10, highest, ubuntu-latest)	43s
checks / test (3.11, lowest-direct, windows-latest)	2m 4s
checks / test (3.10, lowest-direct, windows-latest)	3m 1s
checks / test (3.11, highest, windows-latest)	2m 9s
checks / test (3.11, highest, ubuntu-latest)	44s
checks / test (3.11, lowest-direct, ubuntu-latest)	43s
checks / test (3.12, highest, windows-latest)	2m 51s
checks / test (3.12, highest, ubuntu-latest)	46s
checks / test (3.13, lowest-direct, windows-latest)	2m 10s
checks / test (3.13, lowest-direct, ubuntu-latest)	41s
checks / test (3.12, lowest-direct, windows-latest)	2m 57s
checks / test (3.13, highest, ubuntu-latest)	53s
checks / test (3.13, highest, windows-latest)	2m 5s
checks / test (3.12, lowest-direct, ubuntu-latest)	48s
	26m 0s

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