Update references to php7 to php 8.1

Author: martig7

_docs/developer/testing/install_php.md

@@ -8,7 +8,7 @@ you will need to have PHP installed on your host machine first.
 
 ### Linux & WSL:
 
-*If you're distro cannot find the correct package or installs the wrong version you may have to specify php7.0 in each package name*
+*If you're distro cannot find the correct package or installs the wrong version you may have to specify php8.1 in each package name*
 
 ```bash
 sudo apt-get update

_docs/sysadmin/installation/version_notes/v20.08.00.md

@@ -16,7 +16,7 @@ requires the following edits:
 
 1. Locate your `php.ini` file.
 
-   _It is probably something like `/etc/php/7.2/fpm/php.ini`._
+   _It is probably something like `/etc/php/8.1/fpm/php.ini`._
 
    Note: You can run this command to print your specific version of php:
 
@@ -32,7 +32,7 @@ requires the following edits:
 3. Restart php fpm:
 
    ```
-   sudo systemctl restart php7.2-fpm
+   sudo systemctl restart php8.1-fpm
    ```
 
    Or more generally: