vendor._gowin: Add 'add_preferences' override #3578

Job	Run time
document	49s
smoke (amaranth-lang/amaranth-boards)	36s
test (3.8)	2m 37s
check-links	47s
smoke (amaranth-lang/amaranth-stdio)	39s
test (3.9)	2m 16s
smoke (amaranth-lang/amaranth-soc)	40s
test (3.10)	2m 16s
test (3.11)	2m 52s
test (3.12)	3m 44s
test (pypy-3.8)	5m 4s
test (pypy-3.9)	4m 40s
test (pypy-3.10)	4m 38s
test (3.13-dev)	2m 58s
publish-docs	9s
publish-docs-dev	0s
required	1s
publish-schemas	5s
publish-package	41s
publish-release	0s
	35m 32s

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