Upgrade to PHP 8.1.0 alpha2 release

[agustingomes]

This release fixes an issue when compiling the opcache extension reported here

[mvorisek]

see #1170 and https://github.com/docker-library/php/commits/master/versions.json , I think this update/PR should be done by a bot

[agustingomes]

Thank you for the pointer @mvorisek

I added a comment in the issue regarding why that pipeline might be failing. I think once we merge this, those jobs will succeed since the latest alpha2 version reference is updated here.

Edit: Looking in more detail, the bot does perform the change, so this failure is not related with what I initially thought.

[agustingomes]

I'll close this PR since the update is picked up by a bot.

[mvorisek]

I'll close this PR since the update is picked up by a bot.

I hope so, but I am not sure if that is the case for RCs and when/how the bot is triggered...

[tianon]

We had some issues with the bot thanks to #1166 (docker-library/haproxy#163 (comment)), but the update test build is in progress and should be committed shortly. 👍