Wait for activity completions on worker shutdown (#370) #661

Job	Run time
build-lint-test (3.7, ubuntu-latest)	10m 7s
build-lint-test (3.7, macos-latest)	10m 4s
build-lint-test (3.7, windows-latest)	9m 56s
build-lint-test (3.7, ubuntu-arm)	7m 25s
build-lint-test (3.11, ubuntu-latest)	9m 50s
build-lint-test (3.11, macos-latest)	10m 8s
build-lint-test (3.11, windows-latest)	9m 22s
build-lint-test (3.11, ubuntu-arm)	8m 57s
features-tests / test	10m 21s
	1h 26m 10s

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