Bump postcss from 8.4.39 to 8.4.40 #11598

Job	Run time
Pre run	7s
Lint: CSS	50s
Lint: JS	56s
E2E test: JS (1, 2)	8m 11s
Static Analysis: PHP	0s
E2E test: JS (2, 2)	4m 30s
Unit test: JS	55s
Lint: PHP	0s
Feature tests: PHP ${{ matrix.php }}, WP ${{ matrix.wp }}	0s
Unit test: PHP 8.0, WP latest	23s
Build: ${{ matrix.build }} build ZIP	0s
Unit test: PHP 8.3, WP trunk	24s
Unit test: PHP 8.2, WP trunk	20s
Unit test: PHP 8.1, WP trunk	57s
Unit test: PHP 8.0, WP trunk	22s
Unit test (with coverage): PHP 8.0, WP latest	24s
Unit test: PHP 8.0, WP latest	21s
Unit test: PHP 7.4, WP latest	23s
Unit test: PHP 7.4, WP latest	25s
Unit test: PHP 7.4, WP 6.3	26s
Unit test: PHP 7.4, WP 6.3	24s
Upload plugin ZIPs to Google Cloud Storage	0s
Comment on PR with links to plugin ZIPs	0s
	20m 18s

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