chore(deps): bump postcss and @jupyterlab/builder in /js #147

Job	Run time
build	11s
tests / Load tox environments	6s
visual-regression-tests	0s
tests / codestyle (ubuntu-latest)	13s
tests / py38-test (ubuntu-latest)	2m 13s
tests / py313-test (ubuntu-latest)	2m 15s
tests / py37-test (macos-13)	1s
tests / py310-test (macos-latest)	1s
tests / py312-test (macos-latest)	1s
tests / py39-test (windows-latest)	1m 49s
tests / py311-test (windows-latest)	58s
tests / py38-notebooks (ubuntu-22.04)	2m 22s
tests / py37-notebooks (macos-13)	13s
tests / py39-notebooks (windows-latest)	2m 19s
release	1s
	12m 43s

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