Add php 8 to packages' build matrices; normalize composer reqs

Author: andrewmy

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        php: ['7.3', '7.4']
+        php: ['7.3', '7.4', '8.0']
 
     name: PHP ${{ matrix.php }} tests
 

composer.json

@@ -6,7 +6,7 @@
     "homepage": "https://enqueue.forma-pro.com/",
     "license": "MIT",
     "require": {
-        "php": ">=7.1",
+        "php": "^7.3|^8.0",
         "enqueue/enqueue": "^0.10",
         "queue-interop/queue-interop": "^0.8",
         "symfony/console": "^4.3|^5",