Improve headless browser context isolation #169

Job	Run time
changelog / validate	7s
test / test (windows-latest)	4m 35s
test / validate_declarations (windows-latest)	1m 20s
test / validate_declarations (ubuntu-22.04)	40s
test / validate_metadata (macos-latest)	41s
test / validate_metadata (windows-latest)	1m 27s
test / test (ubuntu-22.04)	2m 31s
test / validate_declarations (macos-latest)	41s
test / test (macos-latest)	3m 3s
test / validate_metadata (ubuntu-22.04)	37s
clean_changelog	-1s
release	58s
	16m 39s

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