build: add php 8.1

Author: Gemorroj

.github/workflows/ci.yml

@@ -37,13 +37,22 @@ jobs:
             composer-flags: '--prefer-lowest'
             job-description: 'Ubuntu; PHP 8.0; lowest-deps'
 
+          - operating-system: 'ubuntu-latest'
+            php-version: '8.1'
+            job-description: 'Ubuntu; PHP 8.1; latest-deps'
+
+          - operating-system: 'ubuntu-latest'
+            php-version: '8.1'
+            composer-flags: '--prefer-lowest'
+            job-description: 'Ubuntu; PHP 8.1; lowest-deps'
+
           - operating-system: 'windows-latest'
-            php-version: '8.0'
-            job-description: 'Windows; PHP 8.0; latest-deps'
+            php-version: '8.1'
+            job-description: 'Windows; PHP 8.1; latest-deps'
 
           - operating-system: 'macos-latest'
-            php-version: '8.0'
-            job-description: 'MacOS; PHP 8.0; latest-deps'
+            php-version: '8.1'
+            job-description: 'MacOS; PHP 8.1; latest-deps'
 
 
     name: ${{ matrix.job-description }}