[DEPS] Also allow v2.0 of `guzzlehttp/promises` #83

Job	Run time
build-source	33s
php-xdebug-docker (7.4, 3.1.5)	52s
php-xdebug-docker (8.0, 3.1.5)	46s
php-xdebug-docker (8.1, 3.1.5)	1m 15s
php-xdebug-docker (8.2, 3.2.1)	46s
confluent-integration (latest)	1m 1s
confluent-integration (4.1.4)	1m 14s
confluent-integration (5.5.2)	1m 0s
ci-checks (7.4, --prefer-lowest)	34s
ci-checks (8.0, --prefer-lowest)	47s
ci-checks (8.1, --prefer-lowest)	30s
ci-checks (8.2, --prefer-lowest)	13s
ci-checks (7.4, --prefer-stable)	41s
ci-checks (8.0, --prefer-stable)	29s
ci-checks (8.1, --prefer-stable)	20s
ci-checks (8.2, --prefer-stable)	39s
	11m 40s

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