chore: version bump built_value and built_value_generator #1250

Job	Run time
test / test-dart-vm (3.0.1)	1m 31s
test / test-dart-vm (stable)	2m 34s
native_test / test-dart-native (macos-latest)	2m 21s
dart2js_test / test-dart-2js (3.0.1, chrome)	1m 52s
ddc_test / test-dart-ddc (3.0.1, chrome)	3m 33s
native_test / test-dart-native (windows-latest)	3m 51s
dart2js_test / test-dart-2js (3.0.1, firefox)	1m 54s
ddc_test / test-dart-ddc (3.0.1, firefox)	2m 3s
dart2js_test / test-dart-2js (stable, chrome)	1m 47s
ddc_test / test-dart-ddc (stable, chrome)	1m 57s
dart2js_test / test-dart-2js (stable, firefox)	1m 52s
ddc_test / test-dart-ddc (stable, firefox)	2m 9s
	27m 24s

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