Build

Improve formatting of code examples in UPGRADE guide #3925

Job	Run time
js-linter	17s
php-linter	23s
phpstan	35s
twig-linter	15s
css-linter	16s
doc-linter	10s
phpunit (ubuntu-latest, 8.1, --prefer-lowest, stable)	1m 47s
phpunit (ubuntu-latest, 8.1, 5.4, stable)	1m 23s
phpunit (ubuntu-latest, 8.5, 7.3, stable)	1m 36s
phpunit (windows-latest, 8.4, 7.3, stable)	3m 56s
phpunit (windows-latest, 8.4, 6.4, stable)	3m 55s
phpunit (ubuntu-latest, 8.3, 7.1, stable)	1m 31s
phpunit (macos-latest, 8.4, 7.3, stable)	2m 59s
phpunit (ubuntu-latest, 8.4, 8.0.x, dev)	1m 29s
phpunit (ubuntu-latest, 8.4, 7.4.x, dev)	1m 35s
phpunit (macos-latest, 8.4, 6.4, stable)	1m 56s
phpunit (ubuntu-latest, 8.4, 7.2, stable)	1m 25s
phpunit (ubuntu-latest, 8.2, 6.4, stable)	1m 41s
	27m 9s

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