Update php to version 8.1

[samuelstein]

php 7.4 support is end of life. therefore update php to old stable

[Pumpapa]

Wholehearted agree that Grav should bump to PHP 8 -- quite a number of skeletons require php 8, so they can fail using docker-grav.
I tried @samuelstein's dockerfile, but that failed with compiler errors

[samuelstein]

Worked on my machine ☺️.
Can you please provide the error?

[Pumpapa]

I'm sorry, maybe I shouldn't have spoken. I compiled on a small Pop OS (Ubuntu) server, which isn't an ideal environment. At the time, I made two screenshots that may contain useful information for you. But sadly I am no longer able to use that machine, so I can't repeat the experiment. Sorry again.

[samuelstein]

@Pumpapa could you please give it a try again? I updated the image.

[YamiDoesDev]

@Pumpapa could you please give it a try again? I updated the image.

Tried it on my machine as well. Didn't notice any problems so far. Thanks for the edit, as I needed php-something >= 8.1 to update my plugins.
I just wonder, if this repository is still maintained?