Allow installing Monolog 3, and run test suite with it

Author: Seldaek

.github/workflows/ci.yaml

@@ -18,6 +18,9 @@ jobs:
                     -   php: '7.4'
                         deps: lowest
                         deprecations: max[self]=0
+                    -   php: '8.1'
+                        deps: highest
+                        monolog: '3.*'
         steps:
             -   name: Checkout
                 uses: actions/checkout@v2

composer.json

@@ -21,7 +21,7 @@
         "symfony/dependency-injection": "^4.4 || ^5.0 || ^6.0",
         "symfony/config": "~4.4 || ^5.0 || ^6.0",
         "symfony/http-kernel": "~4.4 || ^5.0 || ^6.0",
-        "monolog/monolog": "~1.22 || ~2.0"
+        "monolog/monolog": "^1.22 || ^2.0 || ^3.0"
     },
     "require-dev": {
         "symfony/yaml": "~4.4 || ^5.0 || ^6.0",