build: Fix GitHub CI to select alternative and remove PHP 7.4/8.0

It seems update-alternatives used to happen by default but not anymore.
Thus, all builds at https://github.com/wikimedia/less.php/actions/ for
forks and pull-requests silently switched to the same PHP 8.3 build.

Remove PHP 7.4 and 8.0 as those will (correctly) fail after this,
because phpunit 10 and mediawiki-codesniffer 48 requires PHP 8.1
as of Ied6663cf1b (ff0163a) and I3e9c217a49 (c544fa9).

Change-Id: If4836e474c8647d67f5b84cfd3d2bdfafc2e6e7e

Author: Krinkle

.github/workflows/php.yml

@@ -29,29 +29,26 @@ jobs:
         include:
           # Includes php 8.3 and composer 2
           # https://github.com/actions/runner-images/blob/ubuntu24/20250105.1/images/ubuntu/Ubuntu2404-Readme.md#php-tools
-          - php: '7.4'
-            os: ubuntu-24.04
-          - php: '8.0'
-            os: ubuntu-24.04
           - php: '8.1'
-            os: ubuntu-24.04
+            os: ubuntu-latest
           - php: '8.2'
-            os: ubuntu-24.04
+            os: ubuntu-latest
           - php: '8.3'
-            os: ubuntu-24.04
+            os: ubuntu-latest
           - php: '8.4'
-            os: ubuntu-24.04
+            os: ubuntu-latest
 
     runs-on: ${{ matrix.os }}
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Use PHP ${{ matrix.php }}
       run: |
         sudo apt-add-repository ppa:ondrej/php -y
         sudo apt-get install -y -q php${{ matrix.php }} php${{ matrix.php }}-intl php${{ matrix.php }}-mbstring php${{ matrix.php }}-xml php${{ matrix.php }}-apcu php${{ matrix.php }}-curl php${{ matrix.php }}-xdebug
+        sudo update-alternatives --set php /usr/bin/php${{ matrix.php }}
         php --version
 
     - name: Validate composer.json and composer.lock