Speedup PHPUnit tests (#9018) #22692

Job	Run time
Generate the matrix for subscriptions-tests dynamically	1s
WP - nightly \| WC - latest \| wcpay - merchant	15m 3s
WP - nightly \| WC - latest \| wcpay - shopper	38m 5s
WP - nightly \| WC - latest \| subscriptions - merchant	4m 57s
WP - nightly \| WC - latest \| subscriptions - shopper	7m 49s
WC - 7.7.0 \| wcpay - merchant	13m 51s
WC - 7.7.0 \| wcpay - shopper	39m 7s
WC - 7.7.0 \| subscriptions - merchant	5m 4s
WC - 7.7.0 \| subscriptions - shopper	6m 45s
WC - latest \| wcpay - merchant	14m 30s
WC - latest \| wcpay - shopper	39m 40s
WC - latest \| subscriptions - merchant	4m 56s
WC - latest \| subscriptions - shopper	6m 57s
WC - beta \| wcpay - merchant	14m 29s
WC - beta \| wcpay - shopper	40m 51s
WC - beta \| subscriptions - merchant	5m 5s
WC - beta \| subscriptions - shopper	6m 56s
	4h 24m 6s

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