Bump debian from 12.6-slim to 12.7-slim in /postfix #92

Job	Run time
Build and push PHP 7.4	4m 10s
Build and push PHP 8.0	4m 34s
Build and push PHP 8.1	4m 35s
Build and push PHP 8.2	4m 46s
Build and push PHP 8.3	4m 47s
Build and push PHP stable	4m 25s
Build and push nginx	13s
Build and push nginx-proxy	25s
Build and push postfix	2m 22s
Build and push redis	15s
Build and push cron	16s
Build and push mailhog	20s
Build and push mariadb	17s
Build and push newrelic-daemon	13s
	31m 38s

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