vendor._gowin: Add 'add_preferences' override #3581

Job	Run time
document	43s
test (3.8)	2m 20s
check-links	47s
smoke (amaranth-lang/amaranth-boards)	45s
test (3.9)	2m 16s
smoke (amaranth-lang/amaranth-stdio)	50s
test (3.10)	2m 8s
smoke (amaranth-lang/amaranth-soc)	45s
test (3.11)	2m 38s
test (3.12)	3m 30s
test (pypy-3.8)	4m 57s
test (pypy-3.9)	4m 19s
test (pypy-3.10)	4m 33s
test (3.13-dev)	3m 1s
publish-docs	21s
publish-docs-dev	0s
required	1s
publish-schemas	13s
publish-package	48s
publish-release	0s
	34m 55s

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