7.3 isn't actively tested anymore, and since 7.4 has been out for so long already, it doesn't make sense to keep pandering to users who can't be bothered to update their PHP binaries.
In most cases, these users are also experiencing problems caused by older versions of pthreads that were long since fixed.
In addition, pthreads is no longer tested or supported on 7.3, so users can't get newer bug fixes even if they wanted to.
we can't safely use `ubuntu-latest` because the build caches will break if they were built for 18.04 and used on 20.04, or vice versa. Instead, we pin the images (and caches) to a specific version.
commit 1f42169f0f929958f7d68a68f194c6f3492b7eb4
Author: Dylan K. Taylor <odigiman@gmail.com>
Date: Mon Dec 14 21:23:44 2020 +0000
... install it in the right fucking place
commit d2a88abeda5fa937d3f508c4e0300a949af97846
Author: Dylan K. Taylor <odigiman@gmail.com>
Date: Mon Dec 14 21:14:21 2020 +0000
Build PHP using system libraries to reduce rebuild time
